TSKHINVALI, South Ossetia (CNN) -- As fighting continued Sunday between Russia and Georgia over the separatist province of South Ossetia, U.N. officials expressed concern about violence in another Russian-backed breakaway territory in Georgia.
Forces of Abkhazia launched air and artillery strikes on Georgian troops Sunday, intending to drive them out of a small part of Abkhazia that the Georgians controlled, The Associated Press reported.
U.N. Assistant Secretary-General Edmond Mulet said Russian personnel and weapons were part of a military buildup in Abkhazia's capital, Sukhumi. The Georgian government said 4,000 Russian troops have landed in Abkhazia, according to the AP.
Also Sunday, bombing was reported in the Georgian city of Zugdidi, south of the Abkhaz border, "causing panic among the civilian population," Mulet said. Information on casualties and who was responsible for the bombing wasn't available.
"The [U.N.] secretary-general is profoundly concerned over mounting tensions in the Abkhaz zone of conflict," said Lynn Pascoe, U.N. undersecretary-general for political affairs, at an emergency meeting of the Security Council in New York.
Abkhaz forces moved to Abkhazia's border with the rest of Georgia, Mulet said.
The U.S. ambassador to the U.N., Zalmay Khalilzad, told the U.N. Security Council that a Russian-backed military operation in Abkhazia was under way.
Khalilzad also addressed Russia's three-day-old battle with Georgia over South Ossetia, alleging at a Security Council meeting that Russia was trying to overthrow Georgia's government, a former Soviet republic.
Khalilzad told the Security Council that Russian Foreign Minister Sergei Lavrov had told U.S. Secretary of State Condoleezza Rice that Georgian President Mikheil Saakashvili "must go."
Khalilzad then asked Russian Ambassador Vitaly Churkin whether the Russians were seeking "regime change" in Georgia with the military operation they launched Friday. In response, Churkin objected to the disclosure of a confidential phone call between top diplomats and said that "regime change" was "an American expression." Watch Khalilzad's allegation, Churkin's response »
The term was one the Bush administration used to describe its goals in the 2003 invasion of Iraq, which Russia opposed.
Meanwhile, South Ossetia's capital, Tskhinvali, lay in smoldering ruins Sunday after three days of fighting between Georgian and Russian forces.
Each side accused the other of killing large numbers of civilians. Russia said at least 2,000 people have been killed in Tskhinvali.
The Russia-Georgia conflict, which started in South Ossetia last week, continued Sunday, though Georgia began withdrawing its forces from Tskhinvali early that morning.
Georgian troops and their tanks lined the road leading from Tskhinvali back to the positions they held before Thursday. Alexander Lomaia, secretary of Georgia's National Security Council, said the withdrawal was a show of goodwill, aimed at encouraging Russia to accept a cease-fire.
But Russian shells continued to rain on Georgian positions Sunday. Russia insisted Georgia had no plans to stop its military actions, and that its troops were still being shot at Sunday evening.
Moscow also bombed military targets in Tbilisi, with a CNN crew witnessing one strike at a Georgian air base from about 500 yards away.
Alexander Darchiev, spokesman for Russia's Embassy in Washington, described the attacks as "precision strikes against military infrastructure in order to prevent Georgian aircraft and military attack on our peacekeepers."
Also Sunday, Russia said it sank a Georgian missile boat it said was trying to attack Russian ships.
Georgia, a pro-Western ally of the United States, is intent on asserting its authority over South Ossetia and Abkhazia, both of which have strong Russian-backed separatist movements.
The situation in South Ossetia escalated rapidly from Thursday night, when Georgia said it launched an operation into the region after artillery fire from separatists killed 10 people. It accused Russia of backing the separatists.
Speaking to CNN's "Late Edition with Wolf Blitzer," Darchiev called Russia's actions in South Ossetia a peace enforcement.
"We want to force the Georgian leadership to peace, and what we see right now on the ground is that Georgian troops not withdrawing but regrouping, including heavy armor and increased attacks on Tskhinvali," Darchiev said. "Mass mobilization is still under way."
But Saakashvili, Georgia's president, told CNN that his country has "no interest whatsoever in pursuing hostilities." He called on the United States and other nations to stop the "intervention and invasion of my sovereign country."
Bush: U.S. is working for a ceasefire
U.S. President George Bush on Sunday condemned the violence between Russia and Georgia.
"My administration has been engaged with both sides of this trying to get a ceasefire," Bush told NBC's Bob Costas in an interview in Beijing, China, where the president has attended Olympic events.
Vice President Dick Cheney spoke to Saakashvili about the fighting and praised him "for his government's restraint, offers of cease-fire, and disengagement of Georgian forces from the zone of conflict in the South Ossetian region of the country," according to the vice president's office.
"The vice president told President Saakashvili that Russian aggression must not go unanswered, and that its continuation would have serious consequences for its relations with the United States, as well as the broader international community," Lea Anne McBride, press secretary to Cheney, said in a statement.
Georgia begins taking troops out of Iraq
Some of Georgia's 2,000 troops who have been in Iraq returned to Georgia's capital Sunday, Georgian and U.S. officials said.
Georgia asked the United States for an airlift to carry home its troops, which had been stationed near the Iranian border in Iraq. In Baghdad, a U.S. military spokesman confirmed those flights were under way Sunday.
South Ossetia, which has a population of about 70,000, is inside Georgia but has an autonomous government. Many South Ossetians support unification with North Ossetia, which would make them part of Russia.
Russia supports the South Ossetian government, has given passports to many in South Ossetia, and calls them Russian citizens.
Russia has accused Georgia of a genocidal plot to cleanse the region of ethnic Ossetians loyal to Russia. Conversely, Georgia accuses Russia of executing a long-planned war to take control of the region, which has a key pipeline that carries Asian oil to Black Sea ports.
CNN's Matthew Chance in Tskhinvali, Frederick Pleitgen in Tbilisi, Richard Roth and Joe Vaccarello contributed to this report.
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