MONROVIA, Liberia (AP) _ Mortar rounds thudded into the U.S. Embassy compound, homes and a school crowded with refugees in the bloodiest attack on Liberia's besieged capital in days, killing at least 12 Liberian men, women and children.

The onslaught, which wounded more than 100 others, brought despairing new pleas from Monrovia's trapped people for a multinational peace force _ promised for weeks, but still lacking any firm deployment date.

``I want to tell George Bush to do something hurriedly, very fast and quickly,'' cried Emmanuel Sieh, 28, among the frantic crowds that spilled into the streets in front of the U.S. Embassy in this American-founded West African nation after the worst of the daybreak attack.

``People are dying every day,'' Sieh said.

On Friday, President Bush ordered an unspecified number of U.S. troops to be positioned off the coast of Liberia to assist West African peacekeeping forces. Their role and mission will be limited, Bush said.

``We're deeply concerned that the condition of the Liberian people is getting worse and worse and worse,'' Bush told reporters in the Rose Garden. ``Aid can't get to the people. We're worried about the outbreak of disease.''

He said the prime U.S. military role would be to help a force comprised mainly of West African peacekeepers to enter the country, as well as to make it easier for humanitarian aid to be delivered.

Shocked by the bloodiest barrage in days upon Liberia's besieged capital, Monrovia's trapped people took the news of the long-hoped-for U.S. peace deployment with doubt _ even bitterness, that help came after so high a toll.

``Why so late, when people are dying?'' Momo Barley asked in the streets around the U.S. Embassy.

``This is another promise again,'' refugee Sylvester Blamo, 30, said in the same neighborhood, as aid workers tended to lumpily filled body bags.

Liberian government forces and rebels blamed each other for Friday's bombardment, which sent 15 to 20 shells crashing into the densely populated neighborhood around the embassy within 10 minutes.

Refugees have packed into the neighborhood by the thousands, hoping for some safety through proximity to the heavily guarded embassy as rebels press home their three-year war to oust President Charles Taylor.

Taylor, blamed for 14 years of near perpetual conflict in Liberia, has retreated to downtown, his forces battling to block insurgents from crossing bridges into the district.

Mortar barrages during two months of rebel attacks on the city have killed hundreds of refugees. Largely, shells have pounded densely populated neighborhoods rather than strategic targets such as Taylor's mansion or troop concentrations.

One shell Friday struck inside the high-walled U.S. Embassy compound, exploding harmlessly on rocky ground, a U.S. official inside said.

Other rounds brought carnage. One shell at the beginning of the attack slammed into a yard where two boys stood brushing their teeth, killing both.

Blocks away, another shell crashed into the yard of a school where hundreds of people have taken refuge.

The round killed seven refugees outright; an eighth was later reported dead at an international aid group's tent clinic.

At the school, wailing crowds surrounded the dead. Victims' flip-flops lay discarded, soaking in pools of blood. One body, that of a boy in his early teens, lay curled in a corner.

Cradling a 2-week-old baby, a woman sobbed uncontrollably next to a body bag holding the corpse of her sister, the child's mother.

``What do they want to achieve?'' Peter Garwah, 27, cried out, before a new mortar round sent terrified survivors scrambling for cover under schoolhouse tables or pressing, screaming, against classroom walls.

``Innocent people are dying, not soldiers.''

The casualty toll, reported by aid clinics and Monrovia's overwhelmed main hospital, was likely to climb far higher.

An ambulance brought gravely wounded people to the open-air tent hospital run by Medicins Sans Frontieres, also known as Doctors Without Borders.

Workers ferried in the wounded _ a man with a mangled leg; a woman with her intestines spilling out.

In Accra, Ghana, site of off-and-on peace talks and broken cease-fire pledges, rebel envoys accused Taylor's forces of opening the latest fighting _ but called on all sides to stop it.

However, rebel envoys of the main Liberians United for Reconciliation and Democracy movement quarreled publicly before reporters over leadership of their group _ heightening doubts about whether the fraction-plagued organization could make any cease-fire order stick.

West African leaders have promised a multinational force for Liberia since soon after rebels opened offensives in June on the city of 1 million, now crowded with hundreds of thousands of refugees.

Taylor, sought by a U.N.-backed court for alleged war crimes in neighboring Sierra Leone, has promised to step down when foreign peacekeepers arrive. But he has repeatedly hedged on promises since June to cede power.

Regional leaders on Wednesday promised first deployment of Nigerian battalions within seven days. Authorities spoke of setting a firm deployment date Thursday _ but a planning meeting then ended only with announcement of another planning meeting Monday.

Officials in Nigeria, West Africa's military power, say privately that debates over funding of the mission is delaying deployment. The United States has committed at least $10 million to the mission.

On Friday, a woman wrapped in white stood before the U.S. Embassy after the worst of the barrage, raising her arms beseechingly in the air.

``We're tired! We're tired!'' she cried, swaying.

A Marine peered at her through binoculars from the embassy, which has remained staffed throughout the fighting.

Meanwhile, Defense Minister Daniel Chea said rebels had retaken strategic Stockton Bridge overnight. The bridge is one of three key crossings that lead toward downtown; the crossings have been heavily contested since the latest rebel offensive began Saturday.