Republican John McCain said Russia should withdraw its forces. Democrat Barack Obama condemned the violence and urged the two sides to show restraint.

Georgian President Mikhail Saakashvili has long pledged to take back control of South Ossetia, which battled Georgia for de facto independence in fighting that ended in 1992. On Friday, Moscow sent tanks into the region when Georgia launched a major military offensive to retake the breakaway province.

Campaigning in Iowa, McCain told reporters that the U.S. should convene an emergency session of the U.N. Security Council to resolve the crisis.

"What's most critical now is to avoid further confrontation between Russian and Georgian military forces," McCain said.

The U.S. should work with the European Union to put diplomatic pressure on Russia and help establish an independent peacekeeping force in South Ossetia, McCain said.

Obama, flying to Hawaii for a vacation from the campaign trail, issued a statement declaring that "Georgia's territorial integrity must be respected."

"All sides should enter into direct talks on behalf of stability in Georgia, and the United States, the United Nations Security Council, and the international community should fully support a peaceful resolution to this crisis," he said.