The US is to send troops to embattled Georgia in the form of a humanitarian aid exercise, President George Bush said.
Mr Bush said military planes would deliver supplies in a move which would put American forces in the heart of the region.
The president said he was concerned that Russia might be violating the ceasefire in Georgia and he expected all Russian forces to withdraw.
He is also sending Secretary of State Condoleezza Rice to Paris for talks with EU peacemakers and then to Georgia to express solidarity with the democratically elected government there.
Mr Bush spoke after meeting his national security team over the crisis in Russia.
He said he strongly supported France's efforts to broker an end to the fighting.
Mr Bush said said the massive US humanitarian effort was already in progress and would involve US Naval forces as well as aircraft.
A C-17 military cargo plane loaded with supplies was on the way, and Mr Bush said that Russia must ensure that "all lines of communication and transport, including seaports, roads and airports," remain open to let deliveries and civilians through.
"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 said.
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