Hundreds of Haitians ran for cover as gunfire erupted during a march demanding the return of ousted President Jean-Bertrand Aristide (search), leaving three dead in clashes that underscored the tensions in a nation struggling to recover from catastrophic floods.

The shooting broke out Thursday between police and demonstrators, Judicial Police Chief Michael Lucius said. Demonstrators shot and killed three officers, and were believed to have kidnapped a fourth, Justice Minister Bernard Gousse said. No deaths were reported among the marchers.

The violence came as Haitians in the flood-ravaged northwestern city of Gonaives (search) stood in line for hours in the scorching sun waiting for aid workers to hand out drinking water and food.

Nearly two weeks after the flooding from Tropical Storm Jeanne (search), more than 1,550 bodies have been recovered, most in Gonaives, and some 900 are missing, according to government officials.

"It is highly probable that most of the missing are dead," U.N. spokesman Toussaint Kongo-Doudou said.

Several people were wounded by gunfire in Port-au-Prince, Kongo-Doudou said. He said U.N. troops believed a gunfight broke out between Aristide supporters and security guards at shops looted during the march.

Several demonstrators were arrested, the Haitian broadcaster Radio Metropole reported.

Supporters of Aristide, now in exile in South Africa, were commemorating the 13th anniversary of his 1991 ouster by Haiti's army. They also demanded an end to "the occupation" and "the invasion" by foreign troops — referring to the U.S.-led force that followed Aristide's ouster and the U.N. peacekeepers who took over in June.

Thousands of slum dwellers wound through downtown Port-au-Prince carrying photos of Aristide and chanting "Like it or not, Aristide will return!" They passed through a plaza in front of the National Palace and were a few blocks away when shots rang out. Brazilian troops were in armored vehicles nearby, Kongo-Doudou said.

Before the violence, marchers also criticized the U.S. government, chanting "Down with Bush!"

Aristide has accused U.S. agents of kidnapping him when he was flown out of Haiti on a U.S.-chartered jet Feb. 29. The Bush administration insists Aristide left of his own free will.

Aristide, a former slum priest who promised to help the poor, became Haiti's first freely elected president in 1990. He was ousted within months by the army, restored to power by U.S. troops in 1994, then forced to step down by U.S. pressure and a term limit. Aristide was re-elected in 2000.

In February, a street gang in Gonaives known as the Cannibal Army rose up against Aristide, sparking a rebellion joined by soldiers from the former army that Aristide disbanded in 1995.

U.S. troops arrived as Aristide left but did little to disarm rebels, who are demanding the reinstatement of the army and have friendly relations with the U.S.-installed interim government. Rebels also have formed their own political party.

Thursday's violence came a day after scores of rebels arrived at Gonaives' entrance bringing three truckloads of food and offering to help with security.

They were turned back by U.N. peacekeepers who said they could only enter without their guns, rebel commander Remissainthe Ravix said.

Despite that, one group of rebels made it through, and one truckload of their food aid was looted as rebels watched, French police officer Didier Leisigne said.

Food distributions have been slowed by security troubles as hungry crowds have mobbed relief trucks and looted supplies.

Uruguayan troops fired in the air Thursday to keep back a crowd pushing against a truck distributing water.

Francele Henri, 50, said she didn't bother jostling in lines anymore and instead had bought some mushrooms from merchants on credit. "When I go to a distribution I get nothing. There are too many people pushing," she said.

The storm's aftermath has tied up some 750 of the 3,000 U.N. troops in Haiti — less than half the 8,000 originally promised.

An estimated 200,000 people are homeless in Gonaives, many living on sidewalks and rooftops. A thunderstorm soaked the city Thursday and returned slick mud to streets.

The United Nations launched an appeal Thursday for US$30 million in emergency aid. The U.N. World Food Program also said a cargo plane carrying 100 metric tons (110 U.S. tons) of biscuits was arriving Friday from Italy in Port-au-Prince.

Relief workers now have four food distribution centers in Gonaives, giving out some 80 tons of food a day, said Ricardo Mena, of the U.N. Office for the Coordination of Humanitarian Affairs.