Twenty commandos arrived, led by Louis-Jodel Chamblain, a former Haitian soldier who headed army death squads in 1987 and a militia known as the Front for the Advancement and Progress of Haiti, or FRAPH, which killed and maimed scores of people in the early 1990s.
Guy Philippe, a former police chief who fled to the Dominican Republic after being accused by the Haitian government of fomenting a coup in 2002, also arrived in Gonaives to help the rebels prepare for an expected showdown with the government. It was unclear when the volunteers arrived.
Witnesses reached by telephone said the men were working with rebels in Gonaives but were massing in Saint-Michel de l'Atalaye, about 28 miles to the east.
The rebels launched a bloody uprising nine days ago from Gonaives, 70 miles northwest of Port-au-Prince and Haiti's fourth-largest city, seeking President Jean-Bertrand Aristide's ouster. Some 50 people have been killed.
"Chamblain and his men are taking advantage of the situation to further their own ends, ends that would mean the perversion of the democratic movement," said Himler Rebu, an opposition leader and former army colonel who led a failed coup attempt in 1989 against Lt. Gen. Prosper Avril.
He warned the international community that the longer Aristide stays in power, the harder it will be to restore order in Haiti.
Discontent has grown in this Caribbean country of 8 million people since Aristide's party swept flawed legislative elections in 2000 and international donors froze millions of dollars in aid.
However, Secretary of State Colin Powell said Friday the United States and other nations "will accept no outcome that . . . attempts to remove the elected president of Haiti."
The United States sent 20,000 troops to Haiti in 1994 to end a bloody military dictatorship, restore Aristide and halt an exodus of refugees to Florida.
Washington says it plans no new military intervention in the current crisis.
Rebel roadblocks have halted most food and fuel shipments since the unrest began. Emergency supplies of flour, cooking oil and other basics are projected to run out in four days in northern areas, where roadblocks are guarded by rebels who have seized Gonaives and burned police stations in more than a dozen other towns.
Nearby, rebels blocked the road outside Trou-du-Nord leading to the Dominican border at Ouanaminthe. Merchants turned back, saying the barricade of boulders and cars has cut supplies coming from the Dominican Republic, which shares the island of Hispaniola with Haiti.
U.N. representative Adama Guindo appealed to police and rebels to open a "humanitarian corridor." Barricades have blocked deliveries to some 268,000 people dependent on food aid in northern Haiti.
Rebels also have retaken the town of Dondon and burned dozens of houses of Aristide supporters, according to witnesses who fled to the nearby northern port of Cap-Haitien. Police retook the town Feb. 9, when Aristide militants torched nine opposition houses.
Overnight, rebels also attacked police in Saint Suzanne, some 20 miles southwest of Cap-Haitien, according to witnesses reached by telephone.
Haiti has only 5,000 police officers and those manning outlying towns often are outnumbered and outgunned by insurgents.
"The population, which is cut off completely from other parts of the country, is finding itself in a very risky, very dangerous situation," Prime Minister Yvon Neptune said in the capital, Port-au-Prince, which has been unaffected by unrest to the north.
Rebels lit flaming tire barricades early Saturday outside Gonaives and patrolled with rifles amid rumors police were planning to counterattack.
Opposition leaders planned a mass protest in Port-au-Prince on Sunday. On Thursday, Aristide militants crushed a planned anti-government demonstration, stoning opponents and blocking the protest route. Protests have been steady since mid-September.
Opposition politicians refuse to participate in new elections unless Aristide steps down, and the rebels say they will lay down their weapons only when he is ousted.
Many who once backed Aristide have turned on him as poverty deepens while the president's clique enjoys lavish lifestyles that some claim are funded by corruption.
Gas and food prices have more than doubled and more than half the population has fled mounting violence in recent months.
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