Police stormed a volatile slum in the capital Wednesday in an attack on well-armed gangs that witnesses said left at least five people dead — including a pregnant woman and a teenage boy.

The witnesses said the police, some of them masked, fired indiscriminately during the operation in the Bel-Air slum. Police then stood by as men in civilian clothes attacked suspected gang members loyal to ousted President Jean-Bertrand Aristide.

Police spokeswoman Gessy Coicou said the officers raided Bel-Air to arrest gang members but only opened fire because a mob was trying to lynch some of the suspects before they could be arrested. She said one or two people had been killed, but said she had no further details.

One witness, 25-year-old Genel Gilo, said police fired at him and others as they hid inside a house in the massive slum, killing the teenage boy. They brought the youth to U.N. peacekeepers, using a door as a makeshift stretcher, but he died on the way.

"We brought him back here for his family to find him," Gilo said as he stood near the corpse hours after the raid.

Nearby, Peterson Larose, 18, wept as he described how the civilians accompanying the officers stabbed to death his 17-year-old pregnant girlfriend.

Witnesses said the civilians who came with the officers lynched three other people as police watched. Video footage taken by a news agency appeared to support their account.

Human rights groups have long accused Haiti's police force of killing Aristide supporters under the pretext of restoring order to the violent capital.

In a report last month, the human rights group Amnesty international said Haiti's ill-equipped police force executes and arbitrarily arrests people with impunity. It also criticized the U.N. for not preventing such police action.

The 7,600-member peacekeeping mission is intensifying operations to stop a wave of shootings and kidnappings that could threaten November elections meant to replace the interim government set up after the February 2004 rebellion that forced Aristide into exile.