Aid agencies have warned of an imminent humanitarian crisis in the rebel-held area of northern Haiti as unrest continues to spread across the nation.
About 50 people have died in the recent violence
They appealed for swift access to the city of Gonaives and other towns cut off from food convoys and medical care.
About 50 people have been killed in the last week as opposition to the president turned increasingly violent.
On Friday, the US said the removal of Haiti President Jean-Bertrand Aristide was not the way to end the crisis.
US Secretary of State Colin Powell said Mr Aristide's time in power had been disappointing, but "regime change" was not the way forward.
In talks with Canada and Caribbean countries, Mr Powell also discussed sending foreign police to Haiti.
Opposition leaders deny that they are linked to the armed rebel movement of former gang members and disgruntled ex-soldiers which is believed to be in control of about 11 towns and cities across the country.
Both the political opposition and the rebels want the president to resign, accusing him of stealing elections in 2000 and of corruption.
The United Nations World Food Programme said it was unable to deliver supplies to about 268,000 people dependent on food aid in northern Haiti.
Gonaives - Haiti's fourth-largest city with 200,000 residents - has been particularly affected. Virtually no food shipments or medical supplies have reached the city since the unrest began on 5 February.
"What humanitarian workers need now is access to the north," Elisabeth Byrs, UN humanitarian co-ordinator in Geneva, said.
The International Committee of the Red Cross (ICRC) said medical facilities in Gonaives were grinding to a halt as staff feared for their safety and victims of violence were simply scared to seek medical assistance.
"The ICRC is particularly concerned about repeated cases of armed persons entering medical facilities," the agency said in a statement.
"These incursions are posing a growing threat to medical staff and patients alike."
On Friday, Mr Powell said the US was not happy with Mr Aristide's behaviour since US forces restored him to power after a coup a decade ago.
But, he said, Mr Aristide was the democratically elected leader, and that the policy of the administration was not to seek his overthrow.
Democracy had to be respected, Mr Powell said
Mr Powell met Canadian and Caribbean officials of the Caricom inter-governmental group in Washington.
"We will accept no outcome that in any way illegally attempts to remove the elected president of Haiti," Mr Powell told reporters after the talks.
He also said the US, Canada and Caribbean nations were discussing whether foreigners could be sent to bolster Haiti's police.