Liberian rebels have pledged to withdraw from the capital of the war-ruined West African country, a day after Charles Taylor quit as president and went into exile under international pressure.
Washington has not committed itself to using any of its 2,300 Marines aboard warships off Monrovia in a peacekeeping role in Liberia, but a senior US defence official said small groups could be flown into the capital in days ahead to help with tasks such as humanitarian aid.
The official told reporters in Washington he was talking about groups of five or six Marines and that the force's commander, US Army Major General Thomas Turner, had discussed the matter with West African peacekeepers in Monrovia.
"We're talking about small numbers," said the official, asking not to be named. He said other tasks could include medical care for civilians and liaision with the peacekeepers.
Pressed whether larger numbers might go ashore in an emergency to join the fewer than 100 US troops already in Liberia, the official said: "Anything's possible."
But he said there were no current plans to form a Marine "quick reaction force" to fly to the aid of the peacekeepers if heavy fighting broke out between the government and rebels.
The United States is wary of deep involvement given commitments in Afghanistan and Iraq. Memories also live on of a bloody debacle in Somalia a decade ago - the last major US military involvement in Africa.
The LURD rebel group said after a meeting with Turner that by Thursday they would let the West African peacekeepers into Monrovia's vital port, so food could get to hundreds of thousands of famished refugees.