President Bush has directed the U.S. military to lead a humanitarian mission to Georgia where tens of thousands have been forced out of their homes following a Russian invasion last week that has been described by Georgia's president as an "ethnic cleansing."

A U.S. C-17 aircraft with humanitarian supplies already has arrived in the Georgian capital of Tbilisi and another C-17 will arrive there Thursday with additional medical and humanitarian aid, White House spokeswoman Dana Perino said after the president's announcement.

Speaking from the White House Rose Garden with Defense Secretary Bob Gates and Secretary of State Condoleezza Rice, Bush said the aid mission will be "vigorous and ongoing." He warned Russia not to interfere.

"We expect Russia to honor its commitment to let in all forms of humanitarian assistance. We expect Russia to insure that all lines of communication and transport, including seaports, airports, roads and airspace, remain open for the delivery of humanitarian assistance and for civilian transit," Bush said.

The president's announcement was reportedly interpreted by Georgian President Mikheil Saakashvili, a close ally of the United States, to mean that the U.S. military would be taking control of Georgia's ports, but the Pentagon denied that was the case.

"We are not looking to, nor do we need to, take control of any air or sea ports to conduct this mission," Pentagon press secretary Geoff Morrell said.

Bush said he is also sending Rice to Tbilisi, to "personally convey America's unwavering support for the government of Georgia." Rice will travel beforehand to France to meet with French President Nicolas Sarkozy. Perino said Rice was to leave Wednesday evening.

"The United States stands with the democratic government of Georgia and insists that the sovereignty and territorial integrity of Georgia be respected," Bush said. "The United States strongly supports France's efforts as president of the European Union to broker an agreement to end this conflict."

Rice said Russia needs to respect the U.S. aid effort to help the people of Georgia.

"Right now, the key is to remind Russia that it has an obligation to stop its military activities, remind Russia that it is not to further engage in activities that threaten the territorial integrity and sovereignty of Georgia," she said at an afternoon briefing to reporters.

The president spoke after a busy morning of briefings and phone conversations with Sarkozy and Saakashvili.

The administration also spent Wednesday morning trying to document whether Russia is violating the cease-fire it agreed to institute with the former Soviet Republic. FOX News confirmed that Russian tanks entered the city of Gori, just 40 miles from Tbilisi, on Wednesday, after they were supposed to have withdrawn.

"We expect Russia to meet its commitment to cease all military activities in Georgia, and we expect all Russian forces that have entered Georgia in recent days to withdraw from that country," Bush said.

"To begin to repair the damage to its relations with the United States, Europe and other nations, and to begin restoring its place in the world, Russia must keep its word and act to end this crisis," he added.

Perino said that the administration "had credible reports that Russia is violating the cease-fire agreement, including, as (Bush) mentioned, the bombing of vessels and the blocking of the port, which we're very concerned about."

Nearly a week of bombings and rocket attacks has left heavy damage in Georgia. In a conference call with international reporters earlier in the day, Saakashvili predicted a humanitarian disaster, the result of 100,000 people being displaced from their homes in the breakaway regions of South Ossetia and Abkhazia, which Russia wants to claim for itself. He also described "ethnic cleansing" in Gori, and said men and women are being separated and men put in internment camps.

"This is not 1968 and the invasion of Czechoslovakia, where Russia can threaten a neighbor, occupy a capital, overthrow a government and get away with it," Rice said during her briefing. "Things have changed."

Saakashvili said the U.S. and West underestimated Russia's regional ambitions and warned that "America's reputation here, since (the) Cold War, is going to hell now."

"We have been warning them a large scale Russian invasion is coming," Saakashvili said. "(The) State Department told us the Russians are not going to do that."

The Georgian president said Russia's "well planned invasion" is on a larger scale than the first days of the U.S. invasion of Afghanistan in October 2001." He also said he feared Georgia is just the first nation to be subjected to Russia's resurging territorial ambitions.

Saakashvili denied Georgia had provoked the conflict in South Ossetia as Russia has claimed.

"I'm sickened by speculation that Georgia started anything," he said, noting how he had to return to his country while on his way to the Olympics because Georgia had no choice but to "respond or to surrender."

The U.S.-educated Saakashvili credited Republican presidential candidate John McCain with predicting Russia's real intent, but did not make an endorsement in the U.S. presidential campaign.

Rice said she appreciated statements made by both McCain and Democratic presidential candidate Barack Obama.

"I know that they are at this moment of difficult diplomacy that they are doing what they can to support the efforts of the administration," she said.

FOX News' Anne McGinn, Nina Donaghey and The Associated Press contributed to this report.