TBILISI, Georgia -- Concerned by what he called a "dramatic and brutal escalation" of Russian force, President George W. Bush urged Moscow to reverse course in Georgia and withdraw its troops.

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The State Department said it has evacuated more than 170 U.S. citizens from Georgia as the conflict over separatist areas there intensified.

A spokesman said Monday that two convoys carrying about 170 private U.S. citizens along with an undetermined number of family members of American diplomats based in Georgia have left Tbilisi on their way by road to neighboring Armenia. More convoys were being prepared in case other Americans choose to leave Georgia.

The State Department said it would pay for the dependents of U.S. diplomats to leave Georgia if they wanted.

Meanwhile, Georgia's Defense Ministry said Russian armored vehicles rolled into a Georgia military base in the town of Senaki, about 20 miles inland from the Black Sea port of Poti.

The statement appeared to indicate that Russian troops have invaded Georgia proper from the separatist province of Abkhazia while most of the Georgian military forces are locked up in fighting around another breakaway region of South Ossetia.

The Russian attack came as Georgia's president signed a cease-fire pledge. Georgian President Mikhail Saakashvili said Russian warplanes have been bombing roads and bridges and destroyed radar systems earlier Monday.

He said one bombing raid hit near the capital city's airport just a half-hour before international envoys arrived.

Meanwhile, the head of Georgia's national security council said Russian forces have taken the strategically key city of Gori.

By doing so, Saakashvili said Monday, Russian troops have effectively cut the country in half.

Gori is on Georgia's main east-west highway, about 60 miles west of the capital Tbilisi.

Security Council chief Alexander Lomaia said it's not immediately clear if Russian forces will try to advance on Tbilisi.

There have been international calls urging Russia to honor Georgian appeals for a truce.

A State Department official said Secretary of State Condoleezza Rice and the other foreign ministers from the Group of Seven leading industrialized nations spoke by telephone on Monday and pledged their support for a negotiated solution to the conflict.

They called on Russia to respect Georgia's borders and expressed deep concern for civilian casualties that have occurred.

Presidential Candidates Respond

Presidential rivals John McCain and Barack Obama on Monday called for a multi-pronged diplomatic effort to force Russia to withdraw from Georgia, saying Moscow's relationship with the rest of the world depends on it backing down.

Speaking to reporters in Pennsylvania, McCain said Russia appears intent on toppling the Georgian government rather than simply restoring the status quo in the pro-Moscow province of South Ossetia, which Georgia is trying to keep from breaking away.

"We must remind Russia's leaders that the benefits they enjoy from being part of the civilized world require their respect for the values, stability and peace of that world," McCain said.

Obama also urged a multinational response but added that U.N. Security Council should play a major role in helping end the crisis. He said the Security Council should pass a resolution calling for an immediate end to the violence, and urged a U.N. mediator to join French and Finnish foreign ministers in Georgia to try to end the fighting.

"The U.N. must stand up for the sovereignty of its members and peace in the world," Obama told reporters during his weeklong vacation in Hawaii.

Russia's future relationships are at stake, Obama said. An international forum, he said, should be convened to review Russia's interest in joining the World Trade Organization.