The short war has driven tensions between Russia and the West to some of their highest levels since the breakup of the Soviet Union.

A cease-fire signed by the presidents of Russia and Georgia calls for Russian forces to pull back to the positions they held before Aug. 7. The cease-fire allows Russia to maintain troops in a zone extending about 4 miles into Georgia along the South Ossetian border.

The Kremlin said Medvedev told French President Nicolas Sarkozy by phone Tuesday that Russian troops would withdraw from most of Georgia by Friday — some to Russia, others to South Ossetia and a surrounding "security zone" set in 1999.

The White House has made clear that it expects Russia to move faster.

"Both the size and pace of the withdrawal needs to increase, and needs to increase sooner rather than later," National Security Council spokesman Gordon Johndroe said. "I don't think they need any more additional time."

Col. Gen. Anatoly Nogovitsyn, deputy head of the Russian general staff, told a briefing Wednesday that Russia will build a double line of checkpoints totaling 18 in the zone, with about 270 soldiers manning the front-line posts. He said the security zone would be 25 miles from the strategically key city of Gori, but the city is significantly closer to the zone's presumed boundaries than that.

South Ossetia technically remains a part of Georgia, but Russia has said it will accept whatever South Ossetia's leaders decide about their future status — which is almost certain to be either a declaration of independence or a request to be incorporated into Russia.

Western leaders have stressed Georgia must retain its current borders.

"South Ossetia and Abkhazia are part of Georgia," President Bush declared Wednesday in Orlando, Fla., referring to Georgia's two Russian-backed separatist regions.

Russia's foreign minister, Sergey Lavrov, has said the question of Georgia's territorial integrity is a dead issue, a sign that Moscow could try to absorb the two separatist regions.

A U.S. Senate Armed Services Committee delegation, meanwhile, traveled to Georgia to show solidarity with its government and assess the situation after fierce fighting between Georgian and Russian troops.

"We're not going to let this aggression stand. The world is behind you," U.S. Sen. Joe Lieberman, I-Conn., told female refugees during a visit to a center for displaced people in the capital, Tbilisi.

"We can't let a bully do this, because if they do it here, they'll do it other places, and if we don't stop it here we'll have to stop it in a much more difficult way," Lieberman added.