Bush, facing calls for Washington to make its first African foray since a bloody exit from Somalia 10 years ago, said he was working with the United Nations to get government forces and rebels to return to a cease-fire agreed on June 17.
White House spokesman Scott McClellan told reporters Bush had no timetable for a decision on whether to send US peacekeepers as a full understanding of the situation in Liberia was needed first.
A Pentagon spokesman said 4,500 US troops on three warships were being moved into the Mediterranean to place them in a better position for possible use in Liberia, some seven to 10 days sailing time away.
Dozens of mortar bombs slammed into Monrovia's diplomatic quarter Monday. At least one hit the US embassy as rebels fighting to topple President Charles Taylor thrust deep into the coastal capital for the third time in two months.
An angry crowd laid 18 bodies, one of them headless, in front of the embassy and hurled abuse at the mission for not intervening to stop the fighting in a country founded by freed American slaves in the 19th century.
The dead and wounded were mostly among tens of thousands of people who had fled to the heart of Monrovia and the diplomatic quarter where they hoped they would be safe.
US Marines were flown in by helicopter to help defend the embassy and evacuate foreigners. The helicopter crews swivelled machine guns and kept the engines running.
"It shows they value property more than human lives. I hope the rockets hit them in the embassy so they die," said Robita Christopher, demonstrating outside the embassy.
The main rebel faction, Liberians United for Reconciliation and Democracy (LURD), struck into the heart of Monrovia yesterday but government soldiers said they had so far stopped the rebels from crossing two key bridges into the city centre.
Aid workers and witnesses said at least 60 people had been killed by explosions in the sprawling city. Scores of wounded headed to the main hospital.
Both sides accused each other of firing the mortar bombs as the sound of gunfire died down late Monday. US diplomats blamed the rebels, demanding they stop what Washington called indiscriminate shelling of the capital.
LURD said its thrust into Monrovia was not designed to overthrow Taylor but to undermine his capacity to launch attacks which they say he did last week in a cease-fire violation.
Washington has said it might send a small force after the departure of Taylor, accused of fanning more than a decade of regional conflicts and wanted by an international war crimes court. Taylor has agreed to go once peacekeepers arrive.
LURD and another rebel faction hold about two-thirds of Liberia and are bent on ousting Taylor, a former warlord. The rebel groups have their roots in tribal hatreds inflamed by a civil war in the 1990s in which at least 200,000 people died.
Hundreds of civilians were killed during LURD's two previous assaults on the capital last month when aid workers struggled to cope with a massive influx of people to the city centre.
UN Secretary General Kofi Annan and the European Union on Monday urged quick international action to stop the fighting.
"What has the trigger point got to be for someone to act?" demanded Magnus Wolfe-Murray of British medical aid agency Merlin.
- REUTERS
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Liberian rebels shell US complex
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