(CNN) -- Things are moving very fast in Ukraine. Here are Tuesday's developments:
Kerry in Kiev: Russia made up reasons for intervention
U.S. Secretary of State John Kerry on Tuesday accused Russia of making up reasons for intervention in Ukraine, saying that "not a single piece of credible evidence supports any one of these claims."
In the Ukrainian capital of Kiev, where he arrived Tuesday, Kerry said the United States "reaffirms our commitment to Ukraine's sovereignty and territorial integrity under international law" and condemned what he called Russia's aggression in the Ukrainian region of Crimea.
He said it was clear "that Russia has been working hard to create a pretext to invade further" in Ukraine. He said the United States prefers for Russia to de-escalate the crisis but added that if that doesn't happen, "then our partners will have absolutely no choice (but) to join us to continue to expand on steps we have taken in recent days to isolate Russia diplomatically, politically and economically."
Obama: 'Strong belief' that Russia violated international law
President Barack Obama said Tuesday that although Russia has legitimate interests in Ukraine, that doesn't give it a right to exert influence through force.
He said there was a "strong belief" among U.S. and European Union officials that Russia has violated international law by intervening in Ukraine. Obama criticized Russia's arguments that it needs to protect Russian-speaking people there, saying there's been no evidence of serious threats to Russian nationals.
"We have said that if, in fact, there is any evidence out there that Russian speakers or ... Russian nationals are in any way being threatened, there are ways of dealing with that through international mechanisms," Obama said while visiting an elementary school in Washington. "We're prepared to make sure that the rights of all Ukrainians are upheld, and in fact in conversations we've had with the government in Kiev, they have been more than willing to work with the international community and with Russia to provide such assurances."
Ukrainian, Russian officials talking, Yatsenyuk says
Cabinet ministers from Ukraine and Russia have started inter-government consultations, Ukraine's acting Prime Minister Arseniy Yatsenyuk said live on Ukraine's Parliament TV on Tuesday. The talks are going "rather slowly," he said. It's not immediately clear where the talks are happening.
NATO allies meet at Poland's request
NATO allies huddled in Brussels, Belgium, on Tuesday in emergency talks requested by Poland, which considers itself to be under threat by the drama in neighboring Ukraine. Afterward, NATO Secretary General Anders Fogh Rasmussen said that despite repeated calls by the international community, "Russia continues to violate Ukraine's sovereignty and territorial integrity and continues to violate its international commitments."
The developments represent serious implications for the security and stability for the Euro-Atlantic area, he said.
NATO-Russia meeting set for Wednesday
A NATO-Russia meeting is set to take place in Brussels on Wednesday, NATO representative Carmen Romero said. Alexander Grushko, Russia's ambassador to NATO, will be in attendance.
Russia declines invitation to four-nation talks
Russia declined an invitation for talks with Ukraine, a senior U.S. administration official told CNN's Elise Labott on Tuesday, putting a dent in American efforts to find a diplomatic solution to the Crimea crisis. Russia had been invited to Paris for a Wednesday meeting of signatory countries to the 1994 Budapest Memorandum, a pact in which Russia, Ukraine, the United States and the United Kingdom agreed not to threaten or use force against the territorial integrity or political independence of Ukraine.
The document was never signed by the U.S. Senate and therefore is not binding. Nonetheless, Washington has accused Russia of violating the agreement against international law.
U.S. to give $1 billion loan guarantee to Ukraine
Kerry announced that the United States will give Ukraine a $1 billion loan guarantee to help insulate the Ukrainian economy from the effects of reduced energy subsidies from Russia, senior U.S. administration officials said.
The loan guarantee will help Ukraine move forward with an International Monetary Fund assistance package, which calls for it to raise energy prices.
Putin: Russia not claiming Crimea
In a news conference, Russian President Vladimir Putin said the following Tuesday:
On the interim government in Kiev:
• The new government in Ukraine came to power as the result of a coup.
• The ousted President of Ukraine, Viktor Yanukovych, is the legitimate leader of the nation.
• Yanukovych did not give orders to shoot demonstrators
• The parliament in Ukraine is partly legitimate, but the acting President of Ukraine is not.
• Russia is not considering trying to make Crimea a part of Russia.
• He said the troops in Crimea are local "self-defense teams" that "took over control of military bases."
• When asked whether Russia "participated' in Crimea, Putin said no.
• When told by a reporter that the troops blocking the Ukraine army had uniforms similar to Russian uniforms, he said, "Look at the uniforms of other post-Soviet countries. You can see such uniforms in the shop."
• Asked again whether the troops were Russian, he said, "They were self-defense teams. They were prepared very well."
On the use of Russia's military:
• If Russian-speaking citizens in the east of Ukraine ask for Russia's help, Russia has the right "to take all measures to protect the rights of those people." He repeatedly cast any such intervention as a humanitarian mission.
• Military action, he said, would be "completely legitimate" because it was at the request of Yanukovych and in line with Russia's duty to protect people with historic ties to Russia, both cultural and economic.
• Russian military exercises near Ukraine this week were not related to the recent unrest in that country and were planned months ago.
• He sees a double standard by leaders in the United States and other Western countries who have criticized Russia regarding Crimea. He said the United States acted in Afghanistan, Iraq and Libya without a U.N. resolution authorizing that action or by "twisting" U.N. resolutions.
• "I'm not worried that a war will start, because we're not going to go to war with Ukraine. I want you to understand clearly: If we do this, it will only be to protect local people."
Russia says it has ended military exercises near Ukraine's border
Putin ordered troops that took part in military exercises to return to their bases, Russia's state-news agency RIA Novosti reported, citing Dmitry Peskov, the President's press attache. The military exercises took place in the western area of Russia on Monday near the border with Ukraine, and once Putin was briefed on the success of the exercises, he ordered the troops return, Peskov said.
However, Russian troops and vehicles remain near Ukraine's eastern border with Russia, said Sergey Astahov, assistant to the head of the Ukraine Security Border Service. Astahov said Ukrainian security services have not observed the Russian troops themselves, but they are relying on local eyewitnesses who report a continued Russian presence.
Standoff at Crimea's Belbek Air Base
Anxieties have been heightened by a confrontation between Ukrainian soldiers and Russian forces at Belbek Air Base, near Sevastopol.
In footage aired by Crimean Tatar TV, Russian forces were seen firing shots into the air, warning unarmed Ukrainian soldiers from approaching them. The Ukrainians were seen walking toward the Russians carrying a Soviet-era military banner and Ukrainian flag. At one point, a Ukrainian leading the troops refers to the two sides as "brother nations" and calls for negotiations.
The commander of the Belbek base, Yuli Mamchur, said his forces had received a demand to put down their weapons by noon. They refused to comply, he said, adding that it was the latest in long line of demands.
Barriers erected near Crimea military base
A truck arrived at one of Ukraine's main military bases in Simferopol on Tuesday and began to erect concrete barriers in front of the main gate. The workers erecting the barriers told Ukrainian base officials that they received orders from newly installed Crimean authorities to block access to bases where Ukrainian troops and officials have refused to swear allegiance to Crimean authorities, journalist Azad Safarov reported from Kiev.
Ukraine: Armed men harassing personnel at Crimea border checkpoints
Andriy Parubiy, the head of Ukraine's National Security and Defense Council, told the Ukrainian parliament Tuesday that 100 armed men were in a standoff with Ukrainian personnel at the country's border security checkpoints in Crimea and were subjecting them to "psychological attacks." He did not identify these armed men. No shots have been fired, he said.
Parubiy also said the Ukraine government is sending food, water and other essentials to Ukrainian military bases blockaded by Russian forces.
Ukraine denies reports that hundreds of Ukrainian soldiers defected
At least 700 Ukrainian soldiers and officers defected Tuesday, announcing their readiness to defend the population of Crimea, RIA Novosti reported, citing a representative for the newly installed Crimean authority.
In response to this report, the Ukrainian Defense Ministry released a statement saying, "Russian federation continues to publicize through mass media and Internet the untruthful info about defection of Ukrainian military forces in the Crimean territory to the 'Crimean Government,' attempting in this way to justify the unlawful actions on territory of a sovereign state."
Ukraine denies Black Sea flagship has defected
The Ukrainian Consulate told CNN's Ivan Watson that the flagship of the Ukrainian navy's Black Sea fleet, the Ukrainian frigate Hetman Saraidachny, sailed through the Dardanelles on Tuesday morning on its way to Istanbul.
The Consulate denies claims in the Russian media that the ship defected to Russia.
The Consulate was organizing a gathering of Ukrainians on the banks of Istanbul's Bosporus to wave Ukrainian flags and cheer the Ukrainian warship as it steams up the Bosporus toward the Black Sea and presumably Crimea. That was supposed to happen about 8 a.m. ET.
Ukraine OKs $839 million in loans from EU
The Ukrainian parliament ratified an agreement Tuesday to receive loans from the European Union worth 610 million euros, the equivalent of nearly $839 million. The parliament is based in Kiev, where many emphasize ties to the West, as opposed to people in eastern Ukraine, where loyalty to Russia runs deep.
This summary was compiled by CNN's Jason Hanna from reporting from CNN teams in Atlanta, London, Kiev, Moscow and Crimea.