Many Liberians have seen America as their only hope
At least 90 people have been killed in a day of fierce fighting in the besieged Liberian capital, fuelling anger towards the US for failing to send peacekeepers to stop the civil war.
Mortars fell on the diplomatic quarter of Monrovia - killing 60 people alone - as rebels opposed to President Charles Taylor fought for a third day for control of the city.
Bodies of the dead were piled up outside the American Embassy in protest at the delay in bringing in US peacekeepers.
There were moves by Washington to assemble a naval task force but Nigeria
appeared to dash hopes of an early intervention by African peacekeepers.
Nigerian President Olesegun Obasanjo said no Ecowas (Economic Community of West African States) troops would be deployed in Liberia unless there was a ceasefire.
Earlier, an army spokesman in Lagos had said Nigeria was ready to send in a mechanised infantry battalion to act as a buffer force between Liberian government troops and the rebels.
The international relief agency Oxfam appealed on Monday for America to send peacekeepers as part of a multinational umbrella to the state it had helped to found.
"It's terrifying and incredibly frustrating..." said Sam Nagbe, an Oxfam project officer trapped in Monrovia.
"We need international peacekeepers now, not in one month or two months' time."
Ecowas ministers are due to meet US and
European officials in Dakar, Senegal, on Tuesday for talks on peacekeeping options.
Hopes raised and dashed
The rebels, who are seeking to overthrow President Taylor, denied in a BBC interview that they were responsible for Monday's bombardment.
The mortar barrage began as the streets were crowded with people taking advantage of a 12-hour lull in the shelling to try to find water and supplies.
Mutilated and bloodied bodies of around 20 victims were laid out in front of the US Embassy by angry survivors, the BBC's Paul Welsh reports from the city.
They were angry, he says, that America had not led a peacekeeping force to Liberia while there was still a ceasefire to keep.
People who spoke to our correspondent said they had lost faith in a country they used to speak of fondly because it was only interested in looking after its own.
News that America was moving about 4,500 marines and sailors to the Mediterranean for a possible role in Liberia briefly raised spirits until it became clear that it would take two weeks for them to arrive.
Jeers, boos and angry questions began again, our correspondent says.
About 40 American troops did arrive in Monrovia on Monday, landing by helicopter, but they were only there to beef up security at the embassy.
They were flown in from nearby Sierra Leone and the helicopters were later used to evacuate foreign aid workers, including the UN's last seven foreign staff in the country, and journalists back to Freetown.
President George W Bush appeared to suggest on Monday that the US was planning to help deploy an African force rather than send in its own troops.
"We're working with Ecowas to determine when they will be prepared to move in the peacekeeper troops that I have said we would be willing
to help move in to Liberia," he said at his ranch in Texas.
Washington, which is calling for an immediate ceasefire, wants President Taylor to step down but has also warned the Liberians United for Reconciliation and Democracy (Lurd) rebels.
"We've seen this reckless and indiscriminate shelling that has been carried out by the Lurd group," State Department spokesman Philip Reeker
said on Monday.
"We think that's got to stop. There is a ceasefire that needs to be upheld."
Mr Taylor has accepted an offer of asylum from Nigeria but refuses to stand down before the arrival of international peacekeepers.