MONROVIA, Liberia ? Embattled President Charles Taylor accepted an offer of asylum in Nigeria on Sunday, but gave no timeframe for quitting power and insisted the transition must be orderly. He urged the United States to send peacekeepers.

The calls by Taylor and Nigeria’s leader for a peaceful transition increase pressure on President Bush to send U.S. troops to Liberia to enforce a cease-fire in the war-torn nation. Bush heads today to Africa for visits to five nations — including Nigeria, the top powerbroker in West Africa.

Secretary of State Colin Powell telephoned Nigeria’s President Nigerian President Olusegun Obasanjo on Saturday, said State Department spokeswoman Amanda Batt. She did not say what the two discussed.

A team of about 20 U.S. military experts, accompanied by 15 U.S. security troops, left Sunday from a base in southern Spain for Liberia to help assess whether to deploy troops as part of a regional force, as sought by the United Nations, European powers and the Liberians. West African nations have offered 3,000 troops and have suggested that the United States contribute another 2,000.

Taylor is under intense international pressure to step down — Bush has said he would “not take ‘no’ for an answer” — and is holed up in a capital surrounded by rebels. But Taylor has insisted peacekeepers deploy before he will go to ensure fighting does not erupt again.

Another complication is the threat of trial on war crimes charges that hangs over Taylor after his indictment by a U.N.-backed court in Sierra Leone.

The Bush administration reacted coldly to any delay in Taylor quitting.

White House spokesman Jimmy Orr said: “What the president has said is Mr. Taylor needs to leave and leave soon. He needs to leave so peace can be restored.”

One rebel official welcomed the news but said he had no confidence Taylor would follow through and leave Liberia. Taylor has broken promises in the past to step down.

Liberian President Charles Taylor waves at the Roberts International Airport outside the Liberian capital, Monrovia. Taylor on Sunday accepted an offer of asylum in Nigeria but gave no timeframe for leaving power.

“I hope this time around Mr. Taylor will act on his words,” rebel leader Kabineh Ja’neh said in Accra, Ghana. “Far too often he has failed to honor what he says. We don’t trust him. Not at all.”

Taylor and Obasanjo would not say when the Liberian president would step down, but both warned that too hasty a departure could spark new fighting in the West African nation, where hundreds were killed in a failed rebel push into the capital last month.

Taylor added, “It is not unreasonable to request that there be an orderly exit from power.” He said U.S. participation in an international peacekeeping force planned for Liberia was “crucial in every way.”

“We embrace it. We accept it,” he said of the possibility of U.S. involvement in keeping peace in Liberia, founded in the 19th century by freed American slaves.