US Secretary of State Condoleezza Rice says the authorities in Haiti must do more to prepare for presidential and legislative elections on 20 November.
Violence is threatening to destabilise the electoral process
And she appealed to Haitians to register to vote - so far just half of the country's electorate has done so.
She said the poll could mark a turning point in the country's fortunes.
"There is no more powerful weapon in the hands of citizens than the power to vote," she said on a one-day visit to the capital, Port-au-Prince.
Earlier, she met members of the interim government that has been running Haiti since former President Jean Bertrand Aristide was forced into exile in 2004.
In talks with interim President Boniface Alexandre and Prime Minister Gerard Latortue in the capital, Port-au-Prince, Ms Rice expressed concern over planning for legislative and presidential elections.
She said Haiti must increase the number of polling stations and recruit more electoral workers.
The poll "must be open and inclusive and fair", she cautioned.
Condoleezza's visit took place under heavy security
Politically motivated violence has continued in Haiti despite the presence of more than 7,000 United Nations peacekeepers.
A recent report by the human rights group, Amnesty International, says detentions, executions, arbitrary killings, rape and death threats to civilians are routine and perpetrated with impunity.
Ms Rice's visit was not announced until less than 24 hours before her departure in what is seen by experts as a sign of unease about the potential for violence.
Shooting broke out outside the presidential palace in the capital, Port-au-Prince, when former Secretary of State Colin Powell visited Haiti in December 2004.