The crisis in Haiti has had a "devastating effect" on the country's precarious health system, a leading aid expert says.
Haiti's hospitals are struggling to cope with the turmoil
"I am very concerned," Paul Farmer - a Harvard academic who also runs a clinic in Haiti - told the BBC.
The country has been in turmoil for five weeks, following a rebellion that has forced President Jean-Bertrand Aristide into exile.
The UN has appealed for $35m for Haiti, to avert a humanitarian crisis.
"During the past three years, Haiti... has been deprived of all access to international humanitarian assistance," Mr Farmer told the World Today programme.
He said the US administration was responsible for the suspension of aid to Haiti after the disputed 2000 election. "We have all the paper trail on that," he said.
Mr Farmer added that the situation had been "particularly devastating" in the past month.
Haiti's only medical school has been shut down and there have been threats to health care workers in hospitals, he said.
Mr Farmer is a professor at the Harvard Medical School who for 20 years has run a clinic in a slum in central Haiti.
"My own staff are frightened to go to work and also patients are frightened of seeking care," he said.
Last Friday, he went on, rebel soldiers stole two of the clinic's vehicles. They returned on Wednesday, asking for more supplies.
"What we said in response was - don't ask us for things, give us our vehicle back," he said.
Earlier in the week UN emergency relief coordinator Jan Egeland said health and food are the two most immediate priorities in Haiti.
He said the main problems were lack of resources, insecurity and lack of access to parts of the country.
The US and France have deployed troops in Haiti
France and the US have sent 2,500 troops to restore order.
On Wednesday the country's new prime minister, Gerard Latortue, called for national reconciliation and an end to the dictatorships of the past.
He was speaking after arriving back from exile.
Mr Latortue, a former foreign minister and UN official, was appointed to form a transition government and organise fresh elections.