"The president has directed the secretary of defense to position appropriate military capabilities off the coast of Liberia in order to support the deployment of an ECOWAS force once it is generated," the statement said.

The Economic Community of West African States, ECOWAS, is expected to decide Monday on sending a west African peacekeeping force to Liberia, where hundreds of civilians have died in murderous clashes between rebel and government forces.

"The immediate task of the ECOWAS force is to reinforce a ceasefire and begin to create conditions where humanitarian assistance can be provided to the Liberian people," the White House statement said.

"The US role will be limited in time and scope as multinational forces under the United Nations assume the responsibility for peacekeeping and as the United Nations arranges a political transition in Liberia."

"As the United States has said before, Charles Taylor must leave," it added.

Liberian President Charles Taylor was indicted in June by the UN Special Court in Sierra Leone for crimes against humanity and war crimes during the decade-long civil war in Liberia's northwestern neighbour, in which some 250,000 people lost their lives.

Taylor is also under UN sanctions, including an arms embargo, for his perceived role in that war and alleged links to the trade in so-called "blood diamonds" mined by the Sierra Leonean rebels.

The former warlord faces a rebel advance in his own country's devastating four-year war, with the rebels now controlling four-fifths of the country.

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