PORT-AU-PRINCE: Hundreds of foreigners fled Haiti yesterday as American and Canadian warships patrolled offshore in preparation for worldwide economic sanctions aimed at crushing the Caribbean nation's military rulers. Heavy gunfire was heard throughout the night and unidentified gunmen shouted to residents: ''You can come out now. [Exiled President Jean-Bertrand] Aristide won't be coming back.'' The country's international airport was jammed with American and Canadian citizens who were urged to leave Haiti or take security precautions ahead of the anticipated international showdown. Some were missionaries or relief workers who had worked in rural provinces of Haiti, where peasants live in extreme poverty. United States President Bill Clinton's ambassador to the United Nations Madeleine Albright said the US had not ruled out military intervention in Haiti. She said Washington was monitoring the situation closely and was standing by to evacuate 1,000 Americans if necessary. Stringent UN trade sanctions are scheduled to go into effect at noon tomorrow (Hong Kong time) to choke the military's hold on the impoverished country. Half a dozen US warships and three Canadian ships, some visible from the capital city, will make sure that no fuel or arms enter Haiti. The UN sanctions also include freezing the foreign bank accounts of army chief General Raoul Cedras and other military leaders. General Cedras refused to relinquish power as scheduled on Friday, a crucial step in the UN-brokered plan to return democratically-elected Mr Aristide to power on October 30. Many Haitians remained inside their homes, fearful of the police-linked civilian gunmen who, during the past week assassinated the nation's justice minister, threatened US diplomats, terrorised parliament and ordered all ''white foreigners'' to leave thecountry. Only a handful of UN officials and their bodyguards, including special envoy Dante Caputo, remained in Haiti. On Saturday, the US Embassy flew in 30 additional Marine guards, and set up a telephone network to alert the estimated 1,000 American citizens in the country about potential violence. The Canadian Embassy urged all 2,300 of its citizens in Haiti to leave immediately. Late on Saturday night, about 300 pro-military demonstrators gathered near the National Palace to protest against what they called attacks on Haiti's sovereignty. ''Independence or death'' chanted some demonstrators, reviving the popular slogan from the Haitian slave revolution that led to independence from France in 1804. Heavily armed soldiers surrounded the demonstration. Others complained about the street violence that has claimed scores of lives of Aristide supporters in recent weeks. A number of Haitians lined up at the airport to leave the country.