Suspected supporters of exiled Haitian President Jean-Bertrand Aristide sprayed gunfire into a crowd of thousands of jubilant revelers outside the National Palace on Sunday, killing at least six people, including a Spanish journalist, and wounding 18.

Eyewitnesses said gunmen linked to Aristide's Lavalas movement fired from rooftops and burst into the capital's main square in a pickup truck, a jeep and on foot, shooting with automatic weapons into a festive crowd celebrating the fall of the president.

?A whole group from Lavalas came down the Champs de Mars firing in every direction,? said Ingrid Arnesen, a CNN producer who witnessed the attack. ?Heavy machine gun fire.?

It was the boldest attack since Aristide, facing a bloody revolt and international pressure, fled the impoverished Caribbean nation of 8 million last Sunday. His supporters had accused rebel troops of conducting reprisal raids in the capital's slums, home to thousands of Aristide supporters.

Hospital officials said the dead included Spaniard Ricardo Ortega, a correspondent for the Antena 3 Spanish television station. The wounded included two Haiti police officers and American journalist Michael Laughlin of the South Florida Sun-Sentinel newspaper, who was shot in face and shoulder.

US Marines leading an international peace mission roared to the scene in machine gun-mounted Humvees as panicked demonstrators ran for cover and military helicopters hovered over the palace.

<B>Massacre</B>

?It was a massacre,? said Haitian National Police chief Leonce Charles, who was appointed to the job last week.

Prime Minister Yvon Neptune urged police to pursue the ?assassins? no matter what side of Haiti's political divide they came from and said police and foreign troops should start disarming people with illegal weapons.

?I urge all sides to stop the demonstrations until we have a new prime minister and a new government and we can deal with security in the country,? Neptune said at a news conference.

The shootings shattered a largely peaceful demonstration in which thousands took to the streets in a noisy parade to celebrate the fall of Aristide, who fled to Africa. More than 200 people have been killed in the month-long rebellion.

The march, closely watched by US Marines, French troops and Haitian National Police in riot gear, came two days after thousands of angry supporters of Aristide burst out of slums and marched on the US embassy to protest the ?US occupation? and demand his return.

In Sunday's march, revelers hoisted Guy Philippe, the leader of the ragtag band of rebels who helped oust Aristide, on their shoulders, shouting ?Philippe, Philippe!? Another rebel commander, former death squad chief Louis Jodel Chamblain, signed autographs.

Witnesses said the gunfire erupted at street level and from the tops of buildings around the square. Many blamed Aristide's most militant and ruthless supporters, known as the ?chimeres.? ?I saw about a hundred chimeres a couple of blocks from the Champs de Mars,? said Thierry David Henry, a university student attending the rally.