"Our troops are on the highest level of alert. For the last four days we have increased the level of security," General Benjamin Yeaten said.

"We are expecting the next 48 hours to be decisive," he predicted.

Liberia has been wracked by almost non-stop civil war since the 1990s, turning it into one of the world's poorest nations.

The country's warlord-turned-president Charles Taylor, who now controls only a fifth of his country, has agreed to step down and accept asylum in Nigeria but only once an international peacekeeping force is in place.

But rebels from the Liberians United for Reconciliation and Democracy (LURD), who have beseiged the capital, have demanded his immediate resignation.

"We are hearing shelling from Bomi Hills. According to our intelligence we learnt that LURD dissidents have been preparing to attack Monrovia again," Yeaten said.

More than a dozen years of conflict in Liberia have claimed at least 250,000 lives and spread chaos in west Africa, where the fighting has fuelled a humanitarian crisis.

US military experts are currently touring the country to assess humanitarian and security needs in Liberia, which was set up in the nineteenth century as a homeland for America's freed slaves.

There have been repeated calls for US help in setting up a peacekeeping force but US President George Bush has so far refused to make any committments or promise troops for the mission.

Nigeria, Mali and Ghana have already pledged to send 1,500 peacekeepers to the war-torn nation.

WAR.WIRE