Updated

President Bush ordered U.S. ships and troops to take position off the Liberian coast Friday, saying American forces will play a supporting role in bringing peace to the war-torn country.

The command came after a daybreak mortar attack killed at least 26 people and injured more than 200 in Monrovia (search), Liberia's rebel-besieged capital city. One shell hit the grounds of the U.S. Embassy but injured no one.

In Washington, Bush stopped short of saying the Americans would participate directly in the mission to protect Monrovia residents from the fierce fighting.

The U.S. troops' role and mission would be limited, Bush said, but he did not define either. He said he expected the United Nations (search) to relieve the troops "in short order."

"And so our commitment is to enable ECOWAS to go in," he said, referring to peacekeepers from the Economic Community of West African States (search). "And the Pentagon will make it clear over time what that means."

Three Navy ships carrying hundreds of Marines were dispatched to Liberia's coast, Pentagon officials said. It was not clear whether the Marines would enter Liberia (search), where rebels have been battling the government to oust President Charles Taylor, a former warlord.

Bush and senior aides have indicated for some time that the United States probably would get involved. Liberia has a historical relationship with the United States as a country founded by former slaves.

"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."

In New York, United Nations Secretary-General Kofi Annan (search) called Bush's announcement "a very positive development" that should accelerate the deployment of West African peacekeepers.

"I hope it will bring some relief to the people of Liberia," he said.

And once again, Bush called for Liberian President Taylor to leave the country.

The only word from the Pentagon Friday was on the movement of the three ships, led by the USS Iwo Jima (search), an amphibious assault ship that is capable of carrying 1,900 Marines from the 26th Marine Expeditionary Unit, plus 30 helicopters and six to eight AV-8B Harrier fighter planes.

The Iwo Jima was in the Mediterranean, and officials said it would take several days to reach Liberia's coast. The other two ships that will join the Iwo Jima are the USS Nashville, an amphibious transport ship used to launch a landing force of Marines ashore, and the USS Carter Hall, which transports air-cushioned landing craft and other amphibious craft.

In the capital of Monrovia, mortar rounds hit the U.S. Embassy compound, homes and a school crowded with refugees, killing Liberian men, women and children.

"I want to tell George Bush to do something hurriedly, very fast and quickly," cried Emmanuel Sieh, 28, part of a frantic crowd that spilled into the streets in front of the embassy.

"People are dying every day," Sieh said.

The European Command (search), based in Germany and responsible for U.S. military activities in West Africa, said it was sending five people to Nigeria to assess the capabilities of troops in its peacekeeping contingent. The Nigerians are expected to lead the West African peacekeeping mission.

At a picture-taking session with Palestinian Prime Minister Mahmoud Abbas, Bush said the purpose of the mission was "to relieve human suffering."

He also said the cease-fire must be in place.

At the State Department, spokesman Richard Boucher said the United States has made an "initial contribution" of $10 million for a contract with Pacific Architects and Engineers (search) to support the West Africans' troop deployment. "It will include a full range of logistic support to include transportation, equipment and communications," Boucher said.

An earlier White House statement said, "The president has directed the secretary of defense to position appropriate military capabilities off the coast of Liberia" to help support the peacekeeping force.

"The immediate task of the ECOWAS force is to reinforce a cease-fire and begin to create conditions where humanitarian assistance can be provided to the Liberian people," it said.

International relief workers have been pressing the White House for action, saying that a delay in sending in peacekeepers made it impossible to help victims of the fighting.

Taylor has offered to step down and accept haven in Nigeria (search), but has given no time frame and has suggested he would not leave until an international peacekeeping force is in place.

Taylor is sought by a U.N.-backed court for alleged war crimes in neighboring Sierra Leone (search).

Earlier this week, West African foreign ministers meeting in Senegal promised to deploy two Nigerian battalions to Liberia within days — the vanguard of what is expected to be a 3,250-member international force.

The Associated Press contributed to this report.