(CNN) -- Scores of pro-Russian protesters storm a Ukrainian police headquarters and confront the officers inside. Hundreds outside back up the intruders, chanting. A Russian flag flies from the structure as the crowd listens to activists with a megaphone at the entrance.
Monday was the day the Ukrainian government demanded pro-Russian activists give up. Instead, they appear to have overrun another key building in yet another eastern Ukrainian city.
Protesters forced police officers out of their four-story headquarters in the eastern Ukrainian city of Horlivka, witnesses said, adding a new complication for a Kiev government worried about demonstrators' escalating activity in the east and a Russian neighbor that it accuses of fomenting the discontent.
Acting President Oleksandr Turchynov had given pro-Russian protesters in other eastern Ukrainian cities until 2 a.m. ET to disarm or face a "full-scale anti-terrorist operation" by Ukraine's armed forces. But the deadline passed with no sign that it was heeded, including in the eastern city of Donetsk, where protesters have held the regional government building for more than a week.
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A man looks at a bullet shell next to a destroyed car after a gunfight between pro-Russian militiamen and Ukrainian forces in Karlivka, Ukraine, on Friday, May 23. Much of Ukraine's unrest has been centered in the Donetsk and Luhansk regions, where separatists have claimed independence from the government in Kiev.
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Similar deadlines in the past have come and gone with no consequences.
Speaking to CNN's Christiane Amanpour on Monday, Ukraine's U.N. Ambassador Yuriy Sergeyev said it was his understanding the "anti-terrorist operation is in the process."
He talked about the difficulties involved in finding a solution to the crisis, given that women and children are inside the buildings, which -- in turn -- are surrounded by peaceful protesters.
"It's really very difficult to find a solution to avoid the blood. A combination of different approaches should be used," said Sergeyev, calling for dialogue.
A video on online streaming service Ustream purports to show scores of people entering the police headquarters in Horlivka, a city of 300,000. CNN could not independently verify the video.
Outside, a crowd chanted "Referendum!" and "Russia!" A severely beaten man in a police uniform was taken to an ambulance as onlookers shouted at him.
Demonstrators -- some masked, and a few wearing camouflage, but many unmasked and wearing street clothes -- crammed the halls in the video. One room with desks was littered with broken glass.
At one point, a group of men confronted what appeared to be a police officer trying to block their progress in a doorway. The men eventually backed him down, and one of them swung a baton-like object at someone or something, his intended target obscured by onlookers as people shouted and sounds of a struggle ensued. It wasn't clear what happened to the officer.
Officers warned activists to avoid looting. But no officer appeared to stop the masses from walking through the halls and rooms for long.
Horlivka would be at least the 10th city or town in eastern Ukraine where activists have taken over security or government buildings in recent days.
Also Monday, in Slaviansk, Ukrainian authorities appeared to take no action to retake a police station that was occupied earlier. Pro-Russian protesters milled around with makeshift shields outside the building.
When asked why the Ukrainian government had made no apparent move to evict protesters after the deadline passed, Ukrainian Deputy Foreign Minister Danylo Lubkivsky told reporters that the government still believes in a political solution. Although it wants to avoid bloodshed, the government still will protect the country's territorial integrity, he said Monday in Kiev.
Also Monday, U.S. President Barack Obama and Russian President Vladimir Putin spoke about the worsening crisis. The two leaders spoke last March 28.
According to a Russian statement, Putin stressed the protests "are the result of the Kiev authorities' unwillingness and inability to take into account the interests of the Russian and Russian-speaking population," and called on Obama to help prevent the use of force.
"In response to the U.S. President's expressed concern about Russia's alleged interference in southeastern Ukraine, the President of Russia noted that such speculations are based on inaccurate information," it read.
According to the White House, Obama urged Putin to withdraw Russian troops from Ukraine's border and to use his influence to persuade armed pro-Russian groups to leave the buildings they have seized.
"The President noted Russia's growing political and economic isolation as a result of its actions in Ukraine and made clear that the costs Russia already has incurred will increase if those actions persist," the White House said.
Map: Towns in eastern Ukraine affected
Map: Towns in eastern Ukraine affectedKiev blames Moscow
The unrest is the latest in a series of events ratcheting up tensions between Ukraine and Russia, which Kiev accuses of fomenting trouble in Russian-speaking eastern Ukraine.
After then-Ukrainian President Viktor Yanukovych backed out of a deal with the European Union in November in favor of closer ties with Russia, months of protests in Kiev led to his ouster in February.
Distrust among the population in eastern Ukraine, the base of Yanukovych's power, grew as the new national government shifted rapidly in a pro-Western direction. A short time later, pro-Russian elements occupied the Black Sea peninsula of Crimea, which Russia annexed in March. Since then, pro-Russian protesters have taken to the streets in eastern Ukraine and in some cases stormed and occupied buildings.
Kiev's fragile new government and the West accuse Russia of destabilizing the region as a pretext to potentially send in troops to protect the local Russian-speaking population.
NATO says Russian armed forces are massing on Ukraine's eastern border, while Moscow says they are merely carrying out military exercises.
Turchynov on Sunday issued a promise of amnesty for the activists -- including protesters as well as armed militants -- in eastern Ukraine but warned that anyone who continued to support the takeover of government buildings would be held responsible for their actions.
"We'll not allow any repetition of the Crimean scenario in the east of Ukraine," Turchynov said. "I have signed a decree that would allow those who did not shoot at our officers to lay down their arms and leave the occupied buildings by Monday morning without fear of being prosecuted."
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Referendum proposed
After the deadline passed Monday, Turchynov said the majority of Ukrainians would support keeping Ukraine in one piece if a referendum is held along with presidential elections set for May 25.
"We do not mind having a referendum," Turchynov told members of parliament.
"Moreover, if there is (a) parliamentary decision to hold one together with the presidential elections, I am sure most people will express support of independent and unitary Ukraine."
Turchynov has said Russia was responsible for the bloodshed related to the most recent protests. At least one Ukrainian soldier was killed in Sunday clashes between pro-Ukrainian crowds and pro-Russian protesters, a high-level source in Ukraine's Security Services told CNN.
In Moscow, Russian Foreign Minister Sergey Lavrov said any use of force against pro-Russian demonstrators in Ukraine will make it more difficult to create a lasting solution to the crisis.
A stable Ukraine is in Moscow's best interest, Lavrov said, also denying reports that Russian forces are active in the east. He refused to speculate about what events or actions would spur a military intervention by Russia into Ukraine.
Lavrov said he would hold off judgment on Turchynov's proposed referendum until Moscow sees the outline of the questions to be asked. He added that pro-Russian activists in the east must be given an active role in shaping a new constitution.
'Evidence of Russian involvement'
Ukrainian officials have placed blame for unrest in the eastern section of their country squarely on Russia. The new Ukrainian government said it was launching security operations against terrorists who are attempting to "destroy our country."
Giving no further details, it also said it had "concrete evidence of Russian special service involvement" in the pro-Russian protests and storming of buildings and would present it at an international meeting on the Ukraine crisis on Thursday.
Samantha Power, the U.S. ambassador to the United Nations, said Sunday the attacks in Slaviansk were "professional" and "coordinated," similar to Russia's incursion into the Crimean Peninsula last month.
The United States is prepared to step up sanctions against Russia if the recent actions in Ukraine continue, she said. Speaking on ABC's "This Week," she said the latest events in Ukraine bore "the telltale signs of Moscow's involvement."
"I think we've seen that the sanctions can bite. And if actions like the kind that we've seen over the last few days continue, you're going to see a ramping up of those sanctions," she said.
Separately, the United States said a Russian plane made 12 passes near a U.S. Navy warship in the Black Sea on Saturday in the most direct confrontation between the United States and Russia in years.
The plane appeared to be unarmed but passed near the USS Donald Cook several times at both sea level and at several thousand feet.
Pentagon spokesman Col. Steve Warren called the Russian actions "provocative and unprofessional."
On Monday, a Russian Krivak-class frigate was shadowing the same Navy warship in the Black Sea, a U.S. military official said. The frigate remained within sight of the Cook but was not threatening it, the official said.
EU moves to expand sanctions, cutting tariffs for Ukraine
The European Union on Monday moved to widen sanctions and took another step to help Ukraine economically as Kiev's new government seeks closer ties to the West.
"In the European Union we are very strongly committed, as we are in the UK, to the sovereignty and the independence and the territorial integrity of Ukraine," British Foreign Secretary William Hague said in a statement.
"It is very hard to believe after recent events that Russia shares those objectives. I said this morning it is important to have a response and we have agreed among foreign ministers to expand the sanctions -- the second tier of sanctions - and to add further names to those sanctions. So we have taken that decision in the council today," Hague said about the EU's Foreign Affairs Council.
"We have also stressed the urgency of completing the work on a possible third tier of more far-reaching sanctions should those become necessary and the European Commission have assured us that that work is almost complete," he added.
The EU's Foreign Affairs Council also approved tariff cuts for most industrial and all agricultural goods, which will make it cheaper for Ukraine to export them to the European Union, saving Ukraine about €500 million a year, the council said.
The cuts will start at the end of April and last until November 1, by which time a fuller free-trade deal is expected to take effect.
European Union foreign policy chief Catherine Ashton is to meet this week with foreign ministers from the United States, Russia and Ukraine in Switzerland to discuss efforts to de-escalate the situation.
On Sunday night, the U.N. Security Council held an urgent, previously unscheduled meeting to discuss the worsening crisis, where strong condemnations and accusations were traded.
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CNN's Arwa Damon, Khushbu Shah, Steve Almasy and Nick Paton Walsh; journalist Victoria Butenko in Kiev; and journalist Lena Kashkarova in Donetsk contributed to this report
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The body of a pro-Ukrainian militia fighter lies along a road in Karlivka on May 23.
A woman walks past a destroyed car after Ukrainian government forces fired mortar shells during clashes with pro-Russian forces in Slovyansk, Ukraine, on May 23.
A pro-Russian activist carries a ballot box away from a polling station in Donetsk, Ukraine, as he prepares to smash it on May 23.
Local citizens help support a woman at a rally protesting shelling by Ukrainian government forces in the village of Semyonovka, Ukraine, on Thursday, May 22.
Bodies covered with blankets lie in a field near the village of Blahodatne, Ukraine, on May 22, as a Ukrainian soldier smokes next to his armored infantry vehicle.
A Ukrainian soldier rests inside an armored personnel carrier at a checkpoint near Slovyansk on Wednesday, May 21.
Yekaterina Len cries outside her home after it was hit by mortar shells during fighting between pro-Russian separatists and Ukrainian soldiers in Slovyansk on Tuesday, May 20.
A Ukrainian soldier stands guard on the road from Izium, Ukraine, to Slovyansk on Monday, May 19.
A new recruit gets his hair cut at a training camp for the Donbass Battalion, a pro-Ukrainian militia, in the Dnipropetrovsk region of Ukraine on May 19.
Pro-Russian armed militants guard a checkpoint in Slovyansk on May 19, blocking a major highway to Kharkiv.
Pro-Russian militants detain three men on Sunday, May 18, in Kramatorsk, Ukraine. The men are suspected of spying for the Ukrainian government.
A bodyguard of insurgent leader Denis Pushilin stands in front of a statue of Russian revolutionary Vladimir Lenin during a pro-Russia rally in Donetsk on May 18.
Pro-Russian militants guard a checkpoint outside Slovyansk on Saturday, May 17.
Employees of the Ukrainian company Metinvest clear away debris in a government building in Mariupol, Ukraine, on Friday, May 16, after pro-Russian separatists relinquished their hold on it.
Pro-Russian activists argue in Mariupol about how to thwart the upcoming Ukrainian presidential elections.
Pro-Russian gunmen take up positions to fight Ukrainian national troops at a checkpoint outside Slovyansk on Thursday, May 15.
A mortar shell sticks out of the ground at a checkpoint near Slovyansk on May 15.
A man surveys the damage to his home after a mine exploded during an exchange of fire between pro-Russian militants and government troops outside Slovyansk on May 15.
A man examines ballots at a printing house in Kiev, Ukraine, on Wednesday, May 14. The ballots will be used in early presidential voting on May 25.
People collect mortar shells in front of a burnt-out Ukrainian military vehicle near Oktyabrskoe, Ukraine, on May 14.
Two men collect parts of a Ukrainian armored personnel carrier, destroyed May 14 in what the Ukrainian Defense Ministry called a terrorist attack near Kramatorsk.
A member of a "self-defense" squad smashes a slot machine with a sledgehammer Monday, May 12, at an illegal club in Slovyansk.
People celebrate with fireworks in Donetsk on May 12 as separatists declared independence for the Donetsk region.
Roman Lyagin, a member of a rebel election commission, shows referendum results to journalists at a May 12 news conference in Donetsk. Pro-Russian separatists staged the referendum asking residents in the Donetsk and Luhansk regions whether they should declare independence from Ukraine.
An armed pro-Russian separatist takes up a position near Slovyansk on May 12.
A man with a "self-defense" unit checks people's identification in Slovyansk on Sunday, May 11.
A person leaves a voting booth in Luhansk, Ukraine, on May 11. The Donetsk and Luhansk regions of eastern Ukraine voted on controversial referendums to declare independence from the government in Kiev. Acting Ukrainian President Oleksandr Turchynov called the vote "propagandist farce."
Two men react after Ukrainian national guardsmen open fire on a crowd outside a town hall in Krasnoarmiysk, Ukraine, on May 11.
A Ukrainian woman votes at a polling station in Donetsk on May 11.
Ukrainians line up to cast their votes at a polling station in Donetsk on May 11.
A voter casts her ballot in eastern Ukraine's independence referendum in Slovyansk on May 11.
An armed pro-Russian man sits below a flag of the self-proclaimed Donetsk People's Republic at the barricades on a road leading into Slovyansk on May 11.
Black smoke billows from burning tires used to prevent government troops' armored personnel carriers from passing through in Mariupol on Saturday, May 10.
The mother of Dmitriy Nikityuk, who died in a fire at a trade union building during riots in Odessa, Ukraine, cries next to his coffin during his funeral on Thursday, May 8.
A Ukrainian soldier keeps guard at a checkpoint near Slovyansk on May 8.
A pro-Russian activist stands with a Russian national flag outside the regional Interior Ministry building in Luhansk on Wednesday, May 7.
Ukrainian Prime Minister Arseniy Yatsenyuk, right, inspects an armored personnel carrier in Slovyansk on May 7.
An armed pro-Russian separatist takes a position by the railway lines near Slovyansk on Tuesday, May 6.
A relative mourns by the body of 17-year-old Vadim Papura during a service in Odessa on May 6. Papura died after jumping out of a burning trade union building during riots on May 2.
A pro-Russian gunman holds his weapon while guarding the local administration building in Slovyansk on May 6.
Pro-Russian supporters lead blindfolded men in front of the regional administration building in Donetsk on Monday, May 5.
Ukrainian policemen check documents at a checkpoint near the northeastern city of Izium on May 5.
Ukrainian soldiers stand at a checkpoint near Slovyansk on May 5.
Pro-Russian Cossacks sit outside the regional administration building in Donetsk on May 5.
Pro-Russian militants who were arrested during a Ukrainian unity rally are greeted on Sunday, May 4, after being freed by police in Odessa. The men released Sunday had been detained after bloody clashes in Odessa, which ended in a deadly blaze. Forty-six people were killed in the bloodshed.
A pro-Russian militant reacts after being freed on May 4 in Odessa.
Pro-Russian militants clash with police as they storm the police station in Odessa on May 4.
An Orthodox priest, in front of the administration building in Donetsk, blesses a pro-Russian activist May 4 as people gather to honor the memory of fallen comrades in Odessa.
Red carnations are left inside the burned trade union building in Odessa on May 4. Flowers, candles and photos of the dead piled up outside the charred building, a day after brutal clashes and the fire claimed 46 lives.
Pro-Russian protesters light candles in Donetsk on Saturday, May 3, to honor the memory of fallen comrades in Odessa.
A woman cries in front of the burned trade union building in Odessa on May 3.
A man walks past burning tires near Kramatorsk on May 3.
Pro-Russian activists beat a pro-Ukraine supporter trying to save the Ukrainian flag that was removed from a flagpole outside the burned trade union building in Odessa.
Pro-Russian protesters gather in Donetsk to honor the memory of comrades who died in Odessa.
A portrait of Bolshevik leader Vladimir Lenin is part of a barricade in the center of Slovyansk on May 3. The city has become the focus of an armed pro-Russian, anti-government insurgency that aspires to give the eastern regions of Ukraine full autonomy.
A pro-Russian activist sits in front of policemen guarding the burned trade union building in Odessa on May 3.
People lay flowers and candles at the burned trade union building in Odessa on May 3.
Ukrainian soldiers arrive to reinforce a checkpoint that troops seized Friday, May 2, in Andreevka, a village near Slovyansk. Two helicopters were downed Friday as Ukrainian security forces tried to dislodge pro-Russian separatists from Slovyansk, Ukraine's Defense Ministry said.
Police take cover under shields as pro-Russian activists storm the prosecutor's office in Donetsk on Thursday, May 1. Eastern Ukraine was a heartland of support for President Viktor Yanukovych, who was ousted in February.
A pro-Russian activist is wounded after storming the prosecutor's office in Donetsk and clashing with riot police on May 1.
Pro-Russian activists storm the prosecutor's office in Donetsk on May 1. Police fired tear gas and stun grenades in an effort to disperse the activists.
An injured Pro-Russian activist speaks with an armed protester during clashes with police in front of the regional administration building in Donetsk on May 1.
Pro-Russian activists storm an administration building in the center of Luhansk on Tuesday, April 29.
Pro-Russia militants, armed with baseball bats and iron bars, hold flares as they attack people marching for national unity in Donetsk on Monday, April 28.
Detained observers from the Organization for Security and Co-operation in Europe arrive to take part in a news conference Sunday, April 27, in Slovyansk. Vyacheslav Ponomarev, the self-declared mayor of Slovyansk, referred to the observers as "prisoners of war."
Ukrainian troops stand guard behind a barricade made of sandbags at a checkpoint about 30 kilometers (20 miles) from Slovyansk on April 27.
Relatives and friends of a man killed in a gunfight participate in his funeral ceremony in Slovyansk on Saturday, April 26.
U.S. troops arrive at an air force base near Siauliai Zuokniai, Lithuania, on April 26. The United States is conducting military exercises in Poland, Latvia, Estonia and Lithuania. The exercises are, in part, a response to the ongoing instability in Ukraine.
Ukrainian government troops in armored vehicles travel on a country road outside the town of Svyitohirsk in eastern Ukraine on April 26.
Pro-Russia armed militants inspect a truck near Slovyansk on Friday, April 25. Russian Foreign Minister Sergey Lavrov has accused the West of plotting to control Ukraine, and he said the pro-Russia insurgents in the southeast would lay down their arms only if the Ukrainian government clears out the Maidan protest camp in the capital, Kiev.
Pro-Russia militants keep records of their duty in Slovyansk on April 25.
Ukrainian troops take position near burning tires at a pro-Russian checkpoint in Slovyansk on Thursday, April 24.
Ukrainian special forces take position at an abandoned roadblock in Slovyansk on April 24.
A Ukrainian special forces member takes position in Slovyansk.
Cossacks carry a coffin into a church in Slovyansk on Tuesday, April 22, during a funeral for men killed in a gunfight at a checkpoint two days before.
U.S. Vice President Joe Biden, left, talks with Ukrainian Prime Minister Arseniy Yatsenyuk during a meeting in Kiev on April 22.
An armed pro-Russian man stands on a street in Slovyansk on Monday, April 21.
Demonstrators attend a pro-Russian rally outside the secret service building in Luhansk on April 21.
Cars are burned out after an attack at a roadblock in Slovyansk on Sunday, April 20.
A resident inspects burnt-out cars at a roadblock on April 20.
A pro-Russian militant is seen at the roadblock near Slovyansk on April 20.
Armed pro-Russian militants stand guard at a roadblock near Slovyansk on April 20.
A masked man stands guard outside a regional administration building seized by pro-Russian separatists in Slovyansk on Friday, April 18.
People walk around barricades April 18 set up at the regional administration building that was seized earlier in Donetsk.
Russian President Vladimir Putin speaks to the media after a nationally televised question-and-answer session in Moscow on Thursday, April 17. Putin denied that Russian forces are involved in the unrest in eastern Ukraine, though he did say for the first time that Russians were active in Crimea before the peninsula voted to join the country.
Ukrainian riot police officers stand guard during a pro-Ukrainian demonstration in Donetsk on April 17.
Masked pro-Russian protesters stand guard in front of the city hall in Mariupol on April 17.
U.S. Secretary of State John Kerry reaches out to shake hands with Russian Foreign Minister Sergey Lavrov at the start of a bilateral meeting to discuss the ongoing situation in Ukraine. The meeting took place April 17 in Geneva, Switzerland.
A masked gunman stands guard near tanks in Slovyansk on Wednesday, April 16.
A Ukrainian helicopter flies over a column of Ukrainian Army combat vehicles on the way to Kramatorsk on April 16.
A masked pro-Russian gunman guards combat vehicles parked in downtown Slovyansk on April 16.
A man talks with Ukrainian soldiers as they are blocked by people on their way to Kramatorsk.
Ukrainian soldiers sit atop combat vehicles on their way to Kramatorsk.
Ukrainian Gen. Vasily Krutov is surrounded by protesters after addressing the crowd outside an airfield in Kramatorsk on Tuesday, April 15.
Pro-Russian activists guard a barricade April 15 outside the regional police building that they seized in Slovyansk.
Ukrainian troops receive munitions at a field on the outskirts of Izium on April 15.
Armed pro-Russian activists stand guard on top of a Ukrainian regional administration building in Slovyansk on Monday, April 14.
A pro-Russian activist carries a shield during the mass storming of a police station in Horlivka, Ukraine, on April 14.
Russian supporters attend a rally in front of the security service building occupied by pro-Russian activists in Luhansk on April 14.
A man places a Russian flag over a police station after storming the building in Horlivka on April 14.
Men besiege the police station in Horlivka.
The Horlivka police station burns on April 14.
A Ukrainian police officer receives medical care after being attacked at the police station in Horlivka on April 14.
Pro-Russian supporters beat a pro-Ukrainian activist during a rally in Kharkiv on Sunday, April 13.
Pro-Russian activists escort a man outside the secret service building in Luhansk on April 13.
Pro-Russian protesters guard a barricade in Slovyansk on April 13 outside a regional police building seized by armed separatists the day before.
Armed pro-Russian activists carrying riot shields occupy a police station in Slovyansk on April 12.
A group of pro-Russian activists warm themselves by a fire Friday, April 11, in front of a Ukrainian Security Service office in Luhansk.
Ukrainian Prime Minister Arseniy Yatsenyuk speaks April 11 during his meeting with regional leaders in Donetsk. Yatsenyuk flew into Donetsk, where pro-Russian separatists occupied the regional administration building and called for a referendum.
Pro-Russian young men look over the fence of a military recruitment office in Donetsk on Thursday, April 10.
Armed pro-Russian protesters occupy the Security Service building in Luhansk on April 10.
Members of the self-proclaimed government the "Donetsk Republic" vote April 10 during a meeting at the seized regional administration building in Donetsk.
Ukrainian lawmakers from different parties scuffle during a Parliament session in Kiev on Tuesday, April 8.
Workers clean up on April 8 after pro-Russian separatists and police clashed overnight in Kharkiv.
Pro-Russian protesters burn tires near a regional administration building in Kharkiv after police cleared the building on Monday, April 7.
A masked man stands on top of a barricade at the regional administration building in Donetsk on April 7.
Protesters wave a Russian flag as they storm the regional administration building in Donetsk on Sunday, April 6. Protesters seized state buildings in several east Ukrainian cities, prompting accusations from Kiev that Moscow is trying to "dismember" the country.
Pro-Russian protesters clash with police as they try to occupy a regional administration building in Donetsk on April 6.
Pro-Russian activists hold a rally in front of a Ukrainian Security Service office in Luhansk on April 6.
A young demonstrator with his mouth covered by a Russian flag attends a pro-Russia rally outside the regional government administration building in Donetsk on Saturday, April 5.
A Ukrainian soldier guards a road not far from Prokhody, a village near the Russian border, on April 5. Ukrainian and Western officials have voiced alarm about Russia's reported military buildup on Ukraine's eastern border.
Ukrainian cadets at the Higher Naval School embrace a friend who has decided to stay in the school during a departure ceremony in Sevastopol, Crimea, on Friday, April 4. Some 120 cadets who refused to take Russian citizenship left the school to return to Ukraine.
Soviet military veterans take part in a flower-laying ceremony at the Soviet-era World War II memorial in Sevastopol on Thursday, April 3.
Ukrainian soldiers conduct a training session on the Desna military shooting range northeast of Kiev on Wednesday, April 2.
Russian soldiers prepare for diving training in front of a Tarantul-III class missile boat Tuesday, April 1, in Sevastopol.
People pass by barricades near the Dnipro Hotel in Kiev on April 1.
People walk past a train loaded with Russian tanks Monday, March 31, in the Gvardeyskoe railway station near Simferopol, Crimea.
A Russian solder sits in a tank at the Ostryakovo railway station, not far from Simferopol on March 31.
Russian Prime Minister Dmitry Medvedev speaks about the economic development of Crimea during a meeting March 31 in Simferopol.
Members of the Ukrainian National Guard take part in military exercises on a shooting range near Kiev on March 31.
A woman cries Sunday, March 30, during a gathering to honor those who were killed during protests in Kiev's Independence Square.
A woman and child walk past a line of police officers during a rally in Kharkiv on March 30.
Ukrainian soldiers take part in a training exercise at a military base in Donetsk on Saturday, March 29.
Demonstrators protest Friday, March 28, in Kiev, displaying police vehicles they seized during earlier clashes with authorities.
Members of the Right Sector group block the Ukrainian parliament building in Kiev on Thursday, March 27. Activists called for Interior Minister Arsen Avakov to step down after the recent killing of radical nationalist leader Oleksandr Muzychko, who died during a police operation to detain him. Muzychko and the Right Sector are credited with playing a lead role in the protests that toppled Ukrainian President Victor Yanukovych.
Ukrainian tanks are transported from their base in Perevalne, Crimea, on Wednesday, March 26. After Russian troops seized most of Ukraine's bases in Crimea, interim Ukrainian President Oleksandr Turchynov ordered the withdrawal of armed forces from the Black Sea peninsula, citing Russian threats to the lives of military staff and their families.
Ukrainian marines wave as they leave a base in Feodosia, Crimea, on Tuesday, March 25.
Russian sailors stand on the deck of the corvette ship Suzdalets in the bay of Sevastopol on March 25.
Pro-Russian militia members remove a resident as Russian troops assault the Belbek air base, outside Sevastopol, on Saturday, March 22. After its annexation of Crimea, Russian forces have consolidated their control of the region.
Soldiers in unmarked uniforms sit atop an armored personnel carrier at the gate of the Belbek air base on March 22.
A Russian sailor holds the Russian Navy's St. Andrew's flag while standing on the bow of the surrendered Ukrainian submarine Zaporozhye on March 22 in Sevastopol.
Russian President Vladimir Putin signs the final decree completing the annexation of Crimea on Friday, March 21, as Upper House Speaker Valentina Matviyenko, left, and State Duma Speaker Sergei Naryshkin watch.
A Ukrainian serviceman leaves a Ukrainian military unit that Russian soldiers took control of in Perevalne on March 21.
Ukrainian border guards run during training at a military camp in Alekseyevka, Ukraine, on March 21.
Russian soldiers patrol the area surrounding a Ukrainian military unit in Perevalne on Thursday, March 20.
Pro-Russian protesters remove the gate to the Ukrainian navy headquarters as Russian troops stand guard in Sevastopol on Wednesday, March 19.
Pro-Russian forces walk inside the Ukrainian navy headquarters in Sevastopol on March 19.
A member of pro-Russian forces takes down a Ukrainian flag at the Ukrainian navy headquarters in Sevastopol on March 19.
Alexander Vitko, chief of the Russian Black Sea Fleet, leaves the Ukrainian navy headquarters in Sevastopol after pro-Russian forces took it over on March 19.
A Russian flag waves as workers install a new sign on a parliament building in Simferopol, Crimea's capital, on March 19.
Russian military personnel surround a Ukrainian military base in Perevalne on March 19.
Nameplates on the front of the Crimean parliament building get removed Tuesday, March 18, in Simferopol.
From left, Crimean Prime Minister Sergey Aksyonov; Vladimir Konstantinov, speaker of the Crimean parliament; Russian President Vladimir Putin; and Alexei Chaly, the new de facto mayor of Sevastopol, join hands in Moscow on March 18 after signing a treaty to make Crimea part of Russia.
Demonstrators hold a Crimean flag at Lenin Square in Simferopol on March 18.
Ukrainian soldiers stand guard at a checkpoint near Strilkove, Ukraine, close to Crimea on Monday, March 17.
Former boxer and Ukrainian politician Vitali Klitschko addresses reporters in Kiev on March 17.
Ukrainian troops stand guard in front of the Ukrainian Parliament building in Kiev on March 17.
A Ukrainian man applies for the National Guard at a mobile recruitment center in Kiev on March 17.
Civilians walk past riot police in Simferopol on March 17.
A Ukrainian soldier stands on top of an armored vehicle at a military camp near the village of Michurino, Ukraine, on March 17.
Policemen stand guard outside the regional state administration building in Donetsk during a rally by pro-Russia activists March 17.
Armed soldiers stand guard outside a Ukrainian military base in Perevalne on March 17.
A man holds a Crimean flag as he stands in front of the Crimean parliament building in Simferopol on March 17.
Crimeans holding Russian flags celebrate in front of the parliament building in Simferopol on Sunday, March 16.
A Ukrainian police officer tries to shield himself from a road block thrown by pro-Russia supporters in Kharkiv on March 16.
Pro-Russia demonstrators storm the prosecutor general's office during a rally in Donetsk on March 16.
A woman leaves a voting booth in Sevastopol on March 16. See the crisis in Ukraine before Crimea voted
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