Up to 400 peacekeepers raided the Cite Soleil shanty town in central Port-au-Prince and were involved in at least four prolonged shoot-outs, said Lt-Col Jorge Smicelapo, a military spokesman for the Brazilian troops leading the UN mission. "There were many shots exchanged," he told reporters. "It all started early in the morning."
Ernest Erilus, the mayor of Cite Soleil, a no-go area which is populated by the poorest and most desperate Haitians, told Radio Metropole that Emmanuel "Dread" Wilme, was among those killed.
The Haitian police chief, Leon Charles, said he was quite sure Wilme had been killed. "We are not able to give a death toll at this time but we are 80 per cent sure he was killed," he said.
Wilme, who commanded a heavily armed group of young men, was one of the most prominent leaders of the pro-Aristide groups who have been involved in frequent clashes with police and peacekeepers since the forced departure of Mr Aristide in 2004.
If the reports of his death are confirmed - and some reports said he was not dead - Wilme will have been at least the second gang leader killed in Cite Soleil this year. In March, clashes between gangs killed Thomas Robenson, a leader known as "Labanye" who was once allied with Mr Aristide but turned against him before he was ousted.
The peacekeeping mission had been stepping up operations to try to stop growing violence. Last week, they stormed the slum of Bel Air, killing six suspected gang members in a gun battle and freeing a kidnapped female Red Cross employee.
Haiti is preparing for elections this year and there is continuing evidence that Aristide supporters are being subjected to repression and violence by the US-backed government, headed by Gerard Latortue. The 7,000 UN peacekeepers have also been criticised by Aristide supporters and human rights groups for failing to prevent attacks on them by police and even for perpetrating such violence themselves.
Adding to the tension, Guy Philippe, one of the leaders of last year's armed uprising, announced he would run for president, vowing to "change the country and its elite class as well". Mr Philippe, a former police chief in northern Haiti, transformed his rebel army into the National Reconstruction Front party last year, claiming to have 5,000 members. "We will go to elections and I will be the presidential candidate," Mr Philippe told another Haitian radio station.
The secretary general of the Organisation of American States, Jose Miguel Insulza, is on a two-day visit to Haiti to evaluate election preparations. He urged dialogue and reconciliation among Haitian political and social parties, and called on armed forces in the country to stop violence to ensure that the general election could be held as planned.
Mr Insulza has established a voter registration office in Port-au-Prince in an effort to speed a dismally slow registration process. Just 5 per cent, 200,000 of Haiti's 4.5 million eligible voters have registered for the elections, official figures show.
"Haitians should be able to register in great numbers and the registration process should be reliable," Mr Insulza said. "The problem now is to convince Haitians to register to take part in the vote."