Liberian rebels who were fighting to oust warlord President Charles Taylor (search) from power surrendered control of their territory in Monrovia on Thursday, lifting their two-month siege of the starving capital.

The surrender came as U.S. military helicopters touched down at Liberia's main airport and scores of American troops prepared to assist in keeping a peace force in the war-torn country.

As rebels pulled out, more U.S. military helicopters ferried in what was to be 200 Marines and other forces.

U.S. Ambassador John Blaney (search) and rebel chief of staff Abdullah Sherrif (search) shook hands in the center of a bridge marking the front-line of the war-divided capital, signaling the rebel handover.

"We are committed to the peace process," rebel commander Sekou Fofana said after the ceremony.

Some West African peace forces and U.S. Marines crossed into rebel territory after the event. Other peacekeepers held back tens of thousands of civilians massed on both sides of the New Bridge. Many civilians jumped into the swamp water below and swam across.

Tens of thousands of danced, sang and cheered as rebels withdrew. "Thank you! Thank you, America!" many cried.

U.S. fighter jets and helicopters swept back and forth above, drawing roars from the crowds.

At least four West African military vehicles went directly to the vital port that was also given up by the rebels. Control of that port is crucial to getting food and other aid flowing again, particularly to the famished government-held side of the capital.

Firing into the air, rebels bounced out of shelled, bullet-riddled Monrovia in pickup trucks, still clutching their AK-47s and rocket launchers and stereos, sacks of food aid and other loot stolen in the city.

While no rebels could be seen at the port, a few remained on the streets.

Crowds that had been kept inside for weeks under the rebels celebrated and set up market stalls in anticipation of the hungry citizens about to pour across from the government-held side.

Earlier, U.S. Marines donning jungle camouflage and armed with M-16s jumped out as nine U.S. helicopters settled on the tarmac in formation, with two more helicopters hovering overhead.

"We are just here to help the people," said Sgt. Michael Hobbs.

The increased deployment comes after Taylor, a former warlord blamed for 14 years of conflict here, resigned Monday and left the country as demanded by West African leaders, President Bush and the rebels.

Liberia's rebels followed Taylor's departure with an agreement to pull out of the war-divided capital by noon Thursday, ending two months of sieges.

The United States on Wednesday had promised a 150-member "quick reaction" force for Liberia in support of a steadily building West African-led force here.

Another 50 new arrivals are expected to help with the logistics of getting aid flowing again to Liberia's cut-off capital.

"This operation today is going to be an important one," said Blaney, who earlier traveled to the airport to greet the new arrivals. "You are going to see American boots on the ground, and a firm commitment to uphold humanitarian concerns in this country."

The United States previously had only about a dozen American forces in Liberia, serving as liaisons with the 10-day-old West African peace mission.

Taylor's exit has raised hopes for an end to the bloodshed. Fighting since 1989, when Taylor launched the country into civil war, has killed more than 100,000 people, left the once-prosperous country in ruins and left the population prey to armed fighters on both sides who loot and rob.

Washington has stressed that the U.S. role would be as back-up to African peace troops, and that they would be concerned primarily with getting in humanitarian supplies. It doesn't want the Americans to take part in combat.

For Liberians, sight of the American helicopters and troops was enough.

"I am so happy. All these years we've been praying for America to come," said Randolph Eggley, a 51-year-old worker at the airport. "Today maybe peace will begin."

The troops, members of the 26th Expeditionary Unit (search), have been waiting in three U.S. warships off of Liberia and have now pulled to within view of the city.

Heavy looting of U.S. and World Food Program aid warehouses and other stockpiles of food continued Thursday morning ahead of the withdrawal. Thousands of people poured out of the area around the port with bags of grain and other goods on their heads. Rebels fired into the air as looters fought each other for the booty.

The withdrawal would open access to the rebel-held port, allowing food and aid to flow again to residents and rebels on the cut-off and famished government-held side of the capital.

Rebels have demanded that enough peacekeepers be on hand for the turnover to prevent government forces from taking over the port again.

West African nations have been landing peacekeeping troops since Aug. 4, keeping them at a temporary base at the airport until the force reached sufficient strength to deploy in the capital. Monrovia, a city of more than 1 million, is now crowded with hundreds of thousands of refugees.

About 800 West African peacekeepers, mostly Nigerian soldiers, have landed so far, and a second Nigerian battalion was to start flying in later Thursday.

Peace force authorities said at least two Nigerian companies, several hundred men in all, would enter Monrovia by end of day. It was not known if any American forces would go along.

Leaders of Liberia's post-Taylor government said they welcomed the U.S. deployment. "It's long-awaited and we thank God it's been realized," said Lewis Brown, the foreign minister. It "leads one to believe we might be closer to the end."

Brown spoke at the airport as he accompanied new President Moses Blah (search) to Ghana and ongoing peace talks there.

Brown said Blah would meet with leaders of both of Liberia's rebel groups for talks that would focus on their demands that Blah step down.

West African leaders say Blah is to hand over power in October to a transitional government that will lead Liberia to new elections. Rebels insist Blah is only a stand-in for Taylor, and want him out sooner.

A cease-fire has held in Monrovia since the West African peace troops first deployed. Fighting has persisted outside the capital, with recent clashes to the south as Liberia's second rebel group moved forward from the country's second-largest city, the southeastern port of Buchanan.

Blaney, the U.S. ambassador, said the southern rebels have now agreed to withdraw to within a few miles of Buchanan, using the St. John River as a cease-fire line.

The larger rebel group signed a pact Wednesday to withdraw behind the Po River, outside Monrovia.

A second rebel group, based in the south, pledged to pull back to the St. John's River outside the southern city of Buchanan, Blaney said Thursday.

The Associated Press contributed to this report.