PORT-AU-PRINCE -- U.S. troops backed by tanks and helicopters raided the headquarters of Haiti's most feared paramilitary group Monday and detained about 20 people in a dramatic crackdown on civilian gunmen with military links blamed for much of the terror over the last three years.


As helicopters hovered over downtown Port-au-Prince and tanks sealed off the street, American soldiers armed with machine guns raided the dilapidated offices of the Front for the Advancement and Progress of Haiti without firing a shot. A group of Haitian policemen pulling up in a truck were intercepted by U.S. soldiers who forced them to drop their guns and lie on the ground.


Bystanders cheered the action against the paramilitary headquarters from which gunmen opened fire on a pro-democracy march Friday, in which five people were believed killed and several injured, including a Reuters photographer.


The troops detained about 20 people who were put on an army truck, among them a woman who was found to be carrying two guns and a knife in her brassiere and another gun in her pocket. A U.S. source at the scene said those detained in the raid were believed to be minor players in the organization.


Soldiers said they seized weapons, documents and drugs in the building.


The crowd, terrorized by paramilitary gunmen for years, rushed the office and an adjacent bar frequented by the gunmen as soon as the soldiers pulled back. Hundreds of them grabbed stools and chairs, musical instruments and radios, smashing them into tiny pieces in the sidewalk as U.S. soldiers watched.


The raid followed the arrest Sunday of four of the main organizers and weapons suppliers of the "attach?s" or civilian gunmen attached to the Haitian security forces and widely blamed for killings, torture and rape since a bloody coup deposed elected president Jean-Bertrand Aristide in 1991.


The top detainee was Romeo Haloun, a Haitian-American and head of the Black Ninjas, a team of black-masked, machine-gun toting commandos in charge of Haitian military ruler Lieutenant General Raoul Cedras' personal protection.


"We detained four of the primary thugs," the commander of the 21,000 U.S. troops in Haiti, Lieutenant General Hugh Shelton told reporters. "They were known dealers in arms, they were known attach?s, they were known Ninjas."


Shelton said at least 10 leaders and their accomplices had been detained and U.S. troops would go after the paramilitary groups more aggressively if they continued to cause violence trying to obstruct Haiti's return to democracy.


Witnesses said troops in tanks and armored jeeps blocked off a street in central Port-au-Prince on Sunday, seizing Haloun from a vehicle outside a house and taking him away handcuffed in the back of a military truck.


Two other men, believed to be prominent businessmen with ties to the military, were seized at the same time as Haloun and driven away in a separate truck. A U.S. source said prominent businessman Gerry Mourra, accused of being a major paramilitary figure, was detained with Haloun, along with three accomplices described as minor figures in the network of armed thugs.


In the southern town of Les Cayes, an American soldier was shot in the stomach in an exchange of gunfire outside a military compound, marking the first an American soldier has been wounded in Haiti since U.S. troops began arriving two weeks ago to secure the country for a return to democracy.


Shelton said the soldier was approached by armed men in the dark Sunday evening as he went to the bathroom. The soldier was hit by one shot and fired back, apparently killing the two Haitians. The soldier was reported to be in stable condition after surgery aboard a U.S. military hospital ship.