Armed supporters of President Jean Bertrand Aristide threw up roadblocks and looted the Haitian capital on Wednesday in anticipation of a threatened rebel attack.
The US and other governments struggled to keep mediation plans alive, but France called on Aristide to step down so that an international peacekeeping force could be deployed.
The United Nations has meanwhile approved the departure of non-essential staff in Haiti to the neighbouring Dominican Republic, but their planned evacuation, under the supervision of US Marines, was postponed for a day.
US President George Bush said a security force could only be sent after a settlement is reached, and warned potential Haitian refugees against taking to sea.
The rebels - who are also demanding Aristide's ouster and have vowed to seize the capital - cemented their control of northern Haiti with the capture of Tortue Island, police said.
"We want to capture the president to have him tried for charges of high treason, assassination, theft etc," said Guy Philippe, the former police commissioner whose small rebel force - about 150 fighters - has made stunning gains in a three-week insurrection.
However, he said they would lay down their arms if Aristide left office.
"We want to capture the president to have him tried for charges of high treason, assassination, theft etc"
Meanwhile, hundreds of Haitians and foreigners braved masked, anger-prone gang members and rushed to the Port-au-Prince airport hoping to leave. At least two airlines cancelled flights due to deteriorating security and waning hopes for a peaceful solution.
Gunfire and looting were reported in the capital as Aristide's political foes demanded the president's departure as a precondition for any settlement.
Haitians were fleeing: the US Coast Guard said it intercepted a vessel from Gonaive, northern Haiti, in waters off Florida carrying 28 people, including seven crewmen and 21 Haitian refugees.
The boat was commandeered by armed Haitians that included policemen and lower-level government workers.
At least 70 people have been killed and scores wounded as the three-week-old insurgency has spread. There are widespread fears of a bloodbath in Port-Au-Prince amid signs the rebels and pro-Aristide forces are prepared for retributory killing sprees.