GORI — Russia sent hundreds of tanks and troops into the separatist province of South Ossetia and bombed Georgian towns Saturday in a major escalation of the conflict that has left scores of civilians dead and wounded.

Georgia, a staunch American ally, launched a major offensive Friday to retake control of breakaway South Ossetia. Russia, which has close ties to the province and posts peacekeepers there, responded by sending in armed convoys and military combat aircraft.

Russian Foreign Minister Sergey Lavrov told reporters in Moscow that some 1,500 people have been killed, with the death toll rising Saturday.

The figure could not be independently confirmed, but witnesses who fled the fighting said hundreds of civilians had probably died. They said most of the provincial capital, Tskhinvali, was in ruins, with bodies lying everywhere.

The air and artillery bombardment left the provincial capital without water, food, electricity and gas. Horrified civilians crawled out of the basements into the streets as fighting eased, looking for supplies.

Russian General Vladimir Boldyrev claimed in televised comments Saturday that Russian troops had driven Georgian forces out of the provincial capital. Witnesses confirmed that there was no sign of Georgian soldiers in the streets.

Georgia’s President Mikhail Saakashvili proposed a cease-fire Saturday. As part of his proposal, Georgian troops were pulled out of Tskhinvali and had been ordered to stop responding to Russian shelling, said Alexander Lomaia, secretary of his Security Council.

Russia did not immediately respond to Mr. Saakashvili’s proposal. Russian President Dmitry Medvedev had said earlier that Moscow sent troops into South Ossetia to force Georgia into a cease-fire.

Mr. Lomaia said there had been direct fighting between Russian and Georgian soldiers on the streets of Tskhinvali. He estimated that Russia sent 2,500 troops into Georgia. The Russian military has not said how many of its troops were deployed.

Russian military aircraft also bombed the Georgian town of Gori on Saturday. An Associated Press reporter who visited Gori shortly afterward saw several apartment buildings in ruins, some still on fire, and scores of dead bodies and bloodied civilians. The elderly, women and children were among the victims.

“Georgia is facing Russia’s military aggression,” Mr. Saakashvili said, noting that Russian forces were attacking areas outside South Ossetia. “Georgian authorities support a cease-fire and separation of the warring parties.”

It is the worst outbreak of hostilities since the province won de facto independence in a war against Georgia that ended in 1992.

The fighting threatens to ignite a wider war between Russia and Georgia, which accused Russia of bombing its towns, ports and air bases. Georgia, a former Soviet republic with ambitions of joining NATO, has asked the international community to help end what it called Russian aggression.

It also likely will increase tensions between Moscow and Washington, which Mr. Lavrov said should bear part of the blame for arming and training Georgian soldiers.

Moscow has said it needs to protect its peacekeepers and civilians in South Ossetia, most of whom have been given Russian passports. Ethnic Ossetians live in the breakaway Georgian province and in the neighboring Russian province of North Ossetia.

Overnight, Russian warplanes bombed the Vaziani military base on the outskirts of the Georgian capital and near the Baku-Tbilisi-Ceyhan oil pipeline, Georgian Interior Ministry spokesman Shota Utiashvili said. He also said two other military bases were hit, and that warplanes bombed the Black Sea port city of Poti, which has a sizable oil shipment facility.

Georgia, meanwhile, said it has shot down 10 Russian planes, including four brought down Saturday, according to Kakha Lomaya, head of Georgia’s Security Council.

The first Russian confirmation that its planes had been shot down came Saturday from Russian General Anatoly Nogovitsyn, deputy chief of the General Staff, who said two Russian planes were downed. He did not say where or when.

Russian military commanders said 15 peacekeepers have been killed and about 150 wounded. Russian troops went in as peacekeepers but Georgia alleges they now back the separatists.

Russian military spokesman Colonel Igor Konashenkov accused Georgian troops of killing and wounded Russian peacekeepers when they seized Russian checkpoints. Konashenkov’s allegations couldn’t be independently confirmed Saturday.

Russia’s foreign minister said that Georgia brought the airstrikes upon itself by bombing civilians and Russian peacekeepers, and warned that the small Caucasus country should expect more attacks.

“Whatever side is used to bomb civilians and the positions of peacekeepers, this side is not safe and they should know this,” Mr. Lavrov said.

Asked whether Russia could bomb the Georgian capital, Tbilisi, Mr. Lavrov answered: “I don’t think the bombing is coming from Tbilisi, but whatever part of Georgia is used for this aggression is not safe.”

It was unclear what might persuade either side to stop shooting. Both claim the battle started after the other side violated a cease-fire that had been declared just hours earlier after a week of sporadic clashes.

Diplomats have issued a flurry of statements calling on both sides to halt the fighting and called for another emergency session of the U.N. Security Council, its second since early Friday morning seeking to prevent an all-out war.

President Bush said Saturday the outbreak of fighting is endangering peace throughout the volatile region, and he urged an end to the deadly outbreak of violence.

“I’m deeply concerned about the situation in Georgia,” Mr. Bush said in a statement to reporters while attending the Olympics in Beijing. “The attacks are occurring in regions of Georgia far from the zone of conflict in South Ossetia. They mark a dangerous escalation in the crisis.

“The violence is endangering regional peace, civilian lives have been lost and others are endangered. We have urged an immediate halt to the violence and a stand-down by all troops. We call for an end to the Russian bombings, and a return by the parties to the status quo of Aug. 6.”

Russia, which has granted citizenship to most of the region’s residents, appeared to lay much of the responsibility for ending the fighting on Washington.

Georgia, which borders the Black Sea between Turkey and Russia, was ruled by Moscow for most of the two centuries preceding the breakup of the Soviet Union. Georgia has angered Russia by seeking NATO membership — a bid Moscow regards as part of a Western effort to weaken its influence in the region.

Georgia’s President Mikhail Saakashvili, an American-educated lawyer, long has pledged to restore Tbilisi’s rule over South Ossetia and another breakaway province, Abkhazia. Both regions have run their own affairs without international recognition since splitting from Georgia in the early 1990s and have built up ties with Moscow.

Georgia has about 2,000 troops in Iraq, making it the third-largest contributor to coalition forces after the U.S. and Britain. But MR. Saakashvili has called them home in the face of the South Ossetia fighting. The Georgian commander of the brigade in Iraq said Saturday they would leave as soon as transport can be arranged.