Haiti's premier warned of an impending coup amid fears that a two-week uprising had spread to the country's second-largest city, Cap-Haitien.

Prime Minister Yvon Neptune appealed for international aid, but the United States and France expressed reluctance to send troops to put down the rebellion, which has killed at least 57 people.

Police and armed supporters of President Jean-Bertrand Aristide (search) mounted barricades and patrolled the streets of Cap-Haitien (search) on Haiti's north coast on Tuesday. Flights to the city were canceled.

"We are witnessing the coup d'etat machine in motion," Neptune said. He urged the international community "to show it really wants peace and stability."

Aid agencies called for urgent international action, saying Haiti is on "the verge of a generalized civil war." The U.N. refugee agency met with officials in Washington to discuss how to confront a feared exodus of Haitians, though there were no immediate signs of people fleeing.

In Gonaives (search), rebels fired shots into the air to prevent crowds of hungry residents from stampeding several trucks loaded with lentils and millet brought by the aid agency CARE. Associated Press Television News footage showed one woman trampled in the melee. She was taken to a hospital.

The food was the first shipment to reach Gonaives, a city of 200,000 people, since it was taken by rebels who began the revolt Feb. 5.

The brutality of the insurrection was evident in the central city of Hinche (search), where the bullet-riddled body of a policeman lay unburied and rotting outside a police station.

Hinche, at a strategic crossroads in Haiti's agriculture-rich Artibonite (search) district, was seized Monday by some 50 rebels reportedly led by Louis-Jodel Chamblain, the former chief of a paramilitary group that killed and maimed hundreds of people in the early 1990's.

"If the bodyguards of the police chief hadn't fought back he wouldn't have been killed," resident Francoise Joseph told APTN, saying other police were allowed to leave.

About 30 heavily armed police officers barricaded themselves into the nearby town of Mirebalais and nervously scanned the horizon for attackers.

Also Tuesday, airlines in Port-au-Prince canceled flights to Cap-Haitien, a city of 500,000 people, after witnesses in the barricaded city saw a boat approach and rumors swept the town that rebels were about to attack.

"People think the rebels were already in some neighborhoods, and that while they don't control Cap (Haitien), they are there now," said Bruno Firmin, a 27-year-old businessman who spoke to relatives in Cap-Haitien after his flight there was canceled.

Illustrating the problems Aristide faces in holding Cap-Haitien, Firmin said many there would welcome the rebels, despite the fact that their leaders are former military and police officers with infamously bad human rights records.

"I'm not afraid of the rebels, I'm afraid of the Aristide supporters," Firmin said of gangs who have burned homes and attacked opposition supporters in Cap-Haitien.

Aristide was wildly popular when he became Haiti's first freely elected leader in 1990. But he has lost support since his party swept flawed legislative elections in 2000, and is accused of using police and armed militants to stifle dissent.

An American missionary said Aristide supporters had threatened him in the western port of St. Marc (search), where two anti-government supporters were killed Sunday.

Terry Snow said he was threatened Tuesday by 10 Aristide partisans from a gang that he had seen taking direct orders from Aristide.

On Monday, they told him they were going to "kill some bad people." On Tuesday, he was told "If you don't shut up, we'll kill you," he said.

Snow, 39, from Granbury, Texas, told The Associated Press that he has asked his 20 missionaries to leave St. Marc but that he is staying though "we are fearful of the night."

Haiti's 5,000-member police force appears unable to stem the revolt, Neptune conceded Tuesday, asking for help to strengthen the force. Both he and Aristide have stopped short of asking for military intervention.

Secretary of State Colin Powell said Tuesday "there is frankly no enthusiasm right now for sending in military or police forces to put down the violence."

Powell said the international community wants to see "a political solution" and only then would willing nations offer a police presence to implement such an agreement. The European Union urged both sides to come to a compromise.

Powell spoke by telephone with French Foreign Minister Dominique de Villepin, who called an emergency meeting in Paris to weigh the risks of sending peacekeepers and discuss how otherwise to help Haiti, an impoverished former colony that is home to 2,000 French citizens.

De Villepin said it would be difficult to deploy peacekeepers amid the violence. He told French TV that "an intervention force ... implies a stop to the violence, a restart to dialogue. Nothing will be possible in Haiti if there isn't a jolt."

France has 4,000 troops in its Caribbean territories of Martinique and Guadeloupe.

U.N. Secretary-General Kofi Annan said Tuesday the world body plans to "become much more actively engaged" in Haiti's crisis.