TBILISI, Georgia — Russia expanded its bombing blitz to the Georgian capital, deployed ships off the coast and, a Georgian official said, sent tanks from the separatist region of South Ossetia into Georgian territory, heading toward a border city before being turned back.

Russia also claimed its forces sank a Georgian missile boat that was trying to attack Russian ships in the Black Sea, news agencies reported.

The Russian Defense Ministry refused to comment to The Associated Press on the reports of the sinking and Georgian officials could not immediately be reached. If confirmed, it could mark a serious escalation of the fighting that has raged between Russia and Georgia over South Ossetia.

Georgia called a cease-fire and said its troops were retreating Sunday from the disputed province of South Ossetia in the face of Russia's far superior firepower, but Russia said the soldiers were "not withdrawing but regrouping" and refused to recognize a truce.

International envoys headed in to try to end the fighting between Russia and its small U.S.-allied neighbor that erupted last week in the Russian-backed separatist region.

The announcement of a retreat came after Russia expanded its bombing blitz Sunday — targeting the area around the Georgian capital's international airport. Russia also deployed a naval squadron off another of Georgia's separatist regions, Abkhazia, and according to Georgia landed thousands of troops.

Georgian President Mikhail Saakashvili said one of the Russian raids on the airport came a half hour before the arrival of the foreign ministers of France and Finland — in the country to try to mediate.

Georgian Interior Ministry spokesman Temur Yakobashvili said Russian tanks tried to cross from South Ossetia into the territory of Georgia proper, but were turned back by Georgian forces. He said the tanks apparently were trying to approach Gori, but did not fire on the city of about 50,000.

Russia also sent naval vessels to patrol off Georgia's Black Sea coast, but denied Sunday that the move was aimed at establishing a blockade.

The ITAR-Tass news agency quoted a Russian Defense Ministry spokesman as saying that Georgian missile boats twice tried to attack Russian ships, which fired back and sank one of the Georgian vessels.