OUTSIDE TSKHINVALI, Georgia — Russia and small, American-allied Georgia headed toward a wider war Saturday as Russian tanks rumbled into the contested province of South Ossetia and Russian aircraft bombed a Georgian town, escalating a conflict that already has left hundreds dead.

Georgia’s Foreign Ministry said the country was “in a state of war” and accused Russia of beginning a “massive military aggression.” The Georgian parliament approved a state of martial law, mobilizing reservists and ordering government authorities to work round-the-clock.

Russian President Medvedev said that Moscow sent troops into South Ossetia to force Georgia into a cease-fire and prevent Georgia from retaking control of its breakaway region after it launched a major offensive there overnight Friday.

In a meeting with refugees, Prime Minister Putin characterized Georgia’s actions as “complete genocide,” according to his office’s Web site. Mr. Putin also said Georgia had effectively lost the right to rule the breakaway province — an indication Moscow could be preparing to fulfill South Ossetians’ wish to be absorbed into Russia.

The risk of the conflict setting off a wider war also increased Saturday when Russian-supported separatists in another breakaway region, Abkhazia, also targeted Georgian troops by launching air and artillery strikes to drive them out.

President Bush called for an end to the Russian bombings and an immediate halt to the violence.

“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,” Mr. Bush said in a statement to reporters while attending the Olympic Games in Beijing.

Georgia President Saakashvili called it an “unprovoked brutal Russian invasion.”

“This is about annihilation of a democracy on their borders,” Mr. Saakashvili told the British Broadcasting Corp. “We on our own cannot fight with Russia. We want immediate cease-fire, immediate cessation of hostilities, separation of Russia and Georgia and international mediation.”

Mr. Medvedev’s office said Saturday evening that Russia had not received the Georgian cease-fire proposal.

Georgia, an American ally whose troops have been trained by American soldiers, launched the major offensive overnight Friday. Heavy rocket and artillery fire pounded the provincial capital, Tskhinvali, leaving much of the city in ruins.

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

Russian Foreign Minister Sergey Lavrov told reporters Saturday in Moscow that some 1,500 people had been killed in South Ossetia since Friday, with the death toll rising. The figures could not be independently confirmed.

But Tskhinvali residents who survived the bombardment by hiding in basements and later fled the city estimated that hundreds of civilians had died. They said bodies were lying everywhere.

Georgia, a country about the size of South Carolina that 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. Today, Russia has approximately 30 times more people than Georgia and 240 times the area.

Both South Ossetia and Abkhazia have run their own affairs without international recognition since splitting from Georgia in the early 1990s and have built up ties with Moscow. Russia has granted its passports to most of their residents.

Mr. Putin arrived late Saturday in the Russian city of Vladikavkaz to talk to South Ossetian refugees who have fled the fighting. He said there were at least 34,000 refugees.

“The actions of the Georgian powers in South Ossetia are, of course, a crime — first of all against their own people,” Mr. Putin said. “The territorial integrity of Georgia has suffered a fatal blow.”

Russia also laid much of the responsibility for ending the fighting on Washington, which has trained Georgian troops. Washington, in turned, blamed Russia.

“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,” Mr. Bush said in the statement.

White House spokesman Gordon Johndroe said Mr. Bush had spoken with both Messers. Medvedev and Saakashvili. But it was unclear what might persuade either side to stop shooting — both claim the other violated a cease-fire declared Thursday.

Alexander Lomaia, secretary of Georgia’s Security Council, estimated that Russia sent 2,500 troops into Georgia. The Russian military would not comment on the number of troops. By late Saturday, Russian military commanders claimed they had driven Georgian forces out of Tskhinvali, a claim that Saakashvili denied.

Russia’s ambassador to NATO Dmitry Rogozin said “98 percent of Tskhinvali” was in ruins. “Our troops have re-established control over the city,” he said.

Smoke rose from the city, and intermittent artillery shelling and sporadic gunfire could still be heard.

Georgian forces knocked out about 40 Russian tanks around Tskhinvali, said Georgia’s Deputy Interior Minister Eka Sguladze. “Our units are well-equipped with anti-tank rockets, and they thwarted a Russian tank attack,” she told reporters.

Georgia, meanwhile, accused Russia of bombing its air bases and the town of Gori, just outside South Ossetia.

An Associated Press reporter who visited Gori shortly after the Russian airstrikes Saturday 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.

The Russian warplanes appeared to have been targeting a military base in Gori’s outskirts that also was bombed.

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

Georgia said it has shot down 10 Russian planes, including four brought down Saturday, according to Mr. Lomaia. It also claimed to have captured two Russian pilots, who were shown on Georgian television.

Russian Colonel Gen. Anatoly Nogovitsyn, deputy chief of the General Staff, confirmed Saturday that two Russian planes had been shot down, but did not say where or when.

Mr. Lavrov, the Russian foreign minister, said Georgia brought the airstrikes upon itself by bombing civilians and Russian peacekeepers. He 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.

Russian military commanders said 15 peacekeepers have been killed and about 150 wounded in South Ossetia, accusing Georgian troops of killing and wounding Russian peacekeepers when they seized Russian checkpoints. The allegations couldn’t be independently confirmed.

In Abkhazia, the separatist government said it intended to push Georgian forces out of the Kodori Gorge. The northern part of the gorge is the only area of Abkhazia that has remained under Georgian government control. Mr. Lomaia confirmed that Georgian administrative buildings in the Kodori Gorge were bombed, but he blamed the attack on Russia.