Two double rotor US helicopters flew in from from the direction of the ships towards the US embassy in Monrovia's Mamba Point diplomatic area, an AFP reporter said.

A US defence official in Washington said that three amphibious warships loaded with marines were meant as a "powerful message" to Liberia's warring factions.

The official, who asked not to be identified, said there were no plans to send troops ashore but the US warships were positioned close by in case their assistance becomes necessary.

"People in Monrovia can see the ships right off the shore, I would think that would be a pretty powerful message," the official said.

The United States earlier this month despatched three ships -- the USS Iwo Jima, Carter Hall and Nashville -- off the coast of Monrovia with some 3,000 marines on board.

WAR.WIRE