"The objective of the mission is to ensure the protection of US nationals in Mauritania and Liberia," the source said, ruling out a military intervention by land for the moment.

The USS naval vessel Kearsarge, which took part in the Anglo-US offensive in Iraq and was on its way home, was diverted and ordered towards the Gulf of Guinea, he said.

According to the US navy's official website, the Kearsarge can carry both planes and attack helicopters and some 2,000 marines in addition to about 1,200 sailors.

The source said US authorities had made contacts with Senegal, next to Mauritania and close to Liberia, for "logistical support."

The vessel, travelling at a speed of about 21 knots, would reach the Liberian coast sometime in the middle of the coming week, he said.

It will cruise in the area to see how the situation evolves.

More than 500 foreigners were evacuated last Monday from the Liberian capital Monrovia, which has been ringed by rebels fighting President Charles Taylor for four years.

There was a coup attempt in Mauritania last weekend but it was quickly put down by the government.

WAR.WIRE