The leader of Haiti's rebel movement, Guy Philippe, has ordered his fighters to lay down their arms.
There is still much unrest between the rebels and pro-Aristide supporters
Mr Philippe acted after apparently coming under strong pressure from the US embassy in the capital.
The BBC correspondent in Haiti says US soldiers sent to restore order after former President Jean-Bertrand Aristide fled have stepped up their presence.
Increasing numbers of US marines have begun patrolling the capital Port-au-Prince and aid is beginning to arrive.
Urgent need for aid
A plane chartered by the UN children's agency (Unicef) arrived on Wednesday, bringing 30 tons of medical supplies.
The situation is said to be particularly bad in the north, where the rebels have held sway for several weeks.
"There are areas we haven't been able to access for months," said Unicef spokeswoman Marixie Mercado, initially because of floods and then because of the political turmoil.
Oxfam calculates at least 80,000 people in Port-de-Paix and 60,000 in Cap Haitien have no access to clean water.
Aid workers are warning that security must be restored to allow the distribution of urgently needed supplies.
US troops have stepped up their patrols on the streets of Port-au-Prince
As negotiations continued to put in a place an interim government, Haiti's prime minister Yvon Neptune declared a state of emergency.
He said that the looting over the past three weeks had caused more than $3m damage.
US mission expanding
Mr Philippe said he agreed to order the disarmament after receiving a reassurance that the US troops gathered in Haiti would guarantee the protection of the Haitian people.
US marines are securing key sites including the airport, port and presidential palace, but their mission has now expanded "to protect Haitians from reprisal attacks", according to Staff Sergeant Timothy Edwards.
"Now there are foreign troops promising to protect the Haitian people...we will lay down our arms," Mr Philippe, who has declared himself the country's military chief, told a news conference in Port-au-Prince.
His comments are an abrupt change from Tuesday when he said he would take charge of Haiti's military and threatened to arrest the prime minister, saying he had a "moral duty" to ensure peace.
Change of heart
The BBC's Stephen Gibbs in Haiti said Mr Philippe was summoned to the American ambassador's residence in Haiti and given what one source described as "a frank talking-to" in which he was asked, or perhaps ordered, to disarm his rebels.
More than 1,000 US troops are in Haiti as part of an international force authorised by the United Nations, which is expected to grow to about 5,000.
There is some evidence that the US soldiers have already adopted a policing role, our correspondent says.
US marines briefly drove through the capital in a convoy of heavily-armed vehicles. They helped take down some of the road-blocks that still clog the streets, but did not intervene in a gun-fight that took place between pro-Aristide supporters and the police outside the presidential palace.
The political fallout from Mr Aristide's sudden departure is continuing. The Caribbean Community (Caricom) has announced it will not participate in a peacekeeping force in Haiti and expressed concern at allegations that Mr Aristide was forced from office.
The community has called for an independent inquiry into the claims.
The American Secretary of State, Colin Powell, has reiterated that Mr Aristide had left Haiti voluntarily.
Caricom also said its members were extremely disappointed with the UN for failing to act sooner. They said they could not understand why the UN had ignored their earlier requests for a peacekeeping force to be sent to Haiti.