BEIJING - President Bush sought to contain the explosive conflict in Georgia on Sunday as the White House warned that "Russian aggression must not go unanswered."

The crisis over a breakaway province, South Ossetia, appeared to ebb as Georgian troops began retreating and honoring a cease-fire, a claim Russia disputed. U.S. officials said Moscow was only broadening its retaliation against Georgia for trying to take control of the region.

The sheer scope of Russia's military response has the Bush administration deeply worried. Russia on Sunday expanded its bombing blitz in areas of Georgia not central to the fighting.

Vice President Dick Cheney spoke Sunday afternoon with Georgian President Mikhail Saakashvili, Cheney press secretary Lee Ann McBride said. "The vice president expressed the United States' solidarity with the Georgian people and their democratically elected government in the face of this threat to Georgia's sovereignty and territorial integrity," McBride said.

Cheney told 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," McBride said.

A Russian official said more than 2,000 people had been killed in South Ossetia since Friday; the figure could not be confirmed independently.

The president was to end his weeklong stay to Asia by attending a baseball game and other events Monday at the Beijing Olympics. The trip was meant mostly for fun and games — there have been plenty of both. But the fast-moving conflict in Georgia has grabbed his attention.

Bush, pressing international mediation, reached out Sunday to French President Nicolas Sarkozy, who heads the European Union. The two agreed on the need for a cease-fire and a respect for Georgia's integrity, White House spokesman Gordon Johndroe said.

In Washington, the chairman of the Senate Armed Services Committee said the United States must work closely with Europe in condemning Russia's actions.

"We cannot just go out alone on this and talk and act unilaterally. We don't have much impact, I believe, in terms of our unilateral declarations anymore with the administration's approach to the world," said Sen. Carl Levin, D-Mich. "We've got to stand together with European allies."

Georgia, whose troops have been trained by American soldiers, began an offensive to regain control over South Ossetia overnight Friday, launching heavy rocket and artillery fire and air strikes that pounded the provincial capital, Tskhinvali. In response, Russia launched overwhelming artillery shelling and air attacks on Georgian troops.

"We're alarmed by this entire situation, and every escalatory step is a further problem," deputy national security adviser Jim Jeffrey told reporters.

The U.S. military began flying 2,000 Georgian troops home from Iraq after Georgia recalled the soldiers following the outbreak of fighting with Russia. The decision was a timely payback for the former Soviet republic that has been a staunch U.S. supporter and agreed to send troops to Iraq as part of the U.S.-led coalition. Georgia was the third-largest contributor of coalition forces after the U.S. and Britain, and most of its troops were stationed near the Iranian border in southeastern Iraq.

The risk of the conflict setting off a wider war increased when Russian-supported separatists in another breakaway region of Georgia, Abkhazia, launched air and artillery strikes on Georgian troops to drive them out of a small part of the province they control.

Also, Ukraine warned Russia it could bar Russian navy ships from returning to their base in the Crimea because of their deployment to Georgia's coast.

"If those Russian ships leave that port in the Black Sea and if Ukraine decides that it is not going to allow those ships back into that port ... that is a potentially much greater conflagration involving a wider regional area," Levin said.

The White House sought to reassure that the administration — including Secretary of State Condoleezza Rice and Joint Chiefs of Staff Chairman Adm. Mike Mullen — were talking to parties on both sides and trying for a diplomatic solution.

"We hope that there is no further bloodshed. There has been too much bloodshed already," Jeffrey said.

Asked about the possibility of sending the U.S. military or other aid to Georgia, Jeffrey said, "Right now our focus is on working with both sides, with the Europeans and with a whole variety of international institutions and organizations to get the fighting to stop."

Levin, too, did not see the chance of U.S. military involvement, though he said the U.S. needs to make clear to Russia that its action "is way out of line."

"It has to be condemned and the world needs to stand against it," Levin said.

Bush also tended to relations with China, again raising raised concerns to President Hu Jintao about how the host of the summer Olympics treats its own people.

Bush worshipped at a Beijing church and declared China has nothing to fear from expressions of faith. The message had the added punch of coming on China's turf, as Bush has done before.

He managed time for a couple of marquee sporting events. With first lady Laura Bush, daughter Barbara and former President George H.W. Bush, he cheered from the stands of the Water Cube Olympic swimming venue. American Michael Phelps claimed the first of an expected string of gold medals by smashing his own world record in the 400-meter individual medley.

"God, what a thrill to cheer for you!" Bush told Phelps afterward.

At night, Bush watched the eagerly anticipated U.S.-China men's basketball game.

Before the contest, he huddled with U.S. players in a corridor of the Olympic arena, putting his hand in with theirs and joining in a cheer, "One, two, three, U.S.A, go!"

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Associated Press writers Mark S. Smith and Paul Alexander contributed to this report.