Haitian President-elect Michel Martelly has criticised the "desperately slow" pace of reconstruction in his country.
During a visit to Washington, Mr Martelly told US Secretary of State Hillary Clinton he was counting on her to ensure international aid would be used effectively.
Mrs Clinton promised the US would help Haiti "all the way".
More than 600,000 people still live in camps after last year's devastating earthquake in Haiti.
Mrs Clinton said many challenges remained 15 months after the earthquake killed more than 300,00 people, and that revitalising Haiti would take leadership.
She said the US was enthusiastic about Mr Martelly's presidency, which is expected to be confirmed by official results due to be released later on Wednesday.
"I'm very encouraged by the campaign that Mr Martelly ran, his emphasis on the people and their needs, his willingness to be very clear on what he hoped to achieve on their behalf," Mrs Clinton said.
Preliminary results released after the 3 April run-off indicated Mr Martelly secured more than two-thirds of the vote, beating the former first lady, Mirlande Manigat.
But a period of appeal means final official results are not due until later on Wednesday.
Mr Martelly said he would dedicate his first six months in office to tackling the cholera epidemic which has been sweeping the country, getting those still living in tent cities into permanent accommodation and boosting agricultural production.