Haiti's opposition rejected a U.S.-backed peace plan to avert all-out civil war, demanding that President Jean-Bertrand Aristide (search) resign and creating a stalemate that alarmed the international community.

The Democratic Platform coalition (search), a broad alliance of opposition groups, rejected the plan despite last-ditch efforts by Secretary of State Colin Powell to stem a crisis sparked by a three-week uprising by rebels who have overrun the northern half of the country.

A State Department official, speaking on condition of anonymity, said the United States was still working with the parties to win acceptance of the plan. France, meanwhile, was trying to convene a meeting in Paris between Aristide and opposition leaders later in the week.

The plan would have kept Aristide as president, but with diminished powers and a shared government.

"We sent our position (paper) and a signed letter saying 'No' to the proposal," opposition leader Paul Denis told The Associated Press. He said the letters were delivered to David Lee of Canada, the Organization of American States (search) representative in Haiti.

"There will be no more delays. Our answer remains the same. Aristide must resign," said Maurice Lafortune, president of the Haitian Chamber of Commerce that is part of the Democratic Platform.

Even if the opposition coalition had accepted the U.S. peace plan, the rebels still insist they will lay down their arms only when Aristide is out of power.

Aristide, who has accepted the plan, appealed to the world for urgent help and warned of a rising death toll and a new exodus of "boat people" if rebels try to take the capital. At least 70 people have been killed in the three-week uprising, about 40 of them police officers.

"Should those killers come to Port-au-Prince, you may have thousands of people who may be killed," Aristide said. "We need the presence of the international community as soon as possible."

France's U.N. Ambassador Jean-Marc de La Sabliere said diplomats were considering proposing "a police force, or a civilian force" for approval by the U.N. Security Council.

The United States also may seek a U.N. Security Council resolution authorizing dispatch of international peacekeepers to Haiti if a settlement between government and opposition forces is reached, a U.S. official said Tuesday.

Britain and Australia, meanwhile, urged their citizens to get out of Haiti, following similar warnings from the United States, France and Mexico. There are about 30,000 foreigners in the former French colony, 20,000 of them Americans.

The official said Powell talked with French Foreign Minister Dominique de Villepin and expressed support for a French effort to convene a Paris meeting between Aristide and opposition leaders later in the week.

The opposition coalition said it would officially announce its decision Wednesday morning.

International aid groups warned of looming hunger and health crises if the violence is not brought under control.

Human Rights Watch said the international community should consider sending soldiers and police to Haiti, citing the "horrendous human rights records" of some rebel leaders and the "violent and lawless methods" adopted by pro-government gangs.

The U.N. World Food Program said looters had ransacked one of its warehouses in Cap-Haitien on Sunday, after the northern city was seized by rebels.

The agency said it still has sufficient stocks either in Haiti or on the way, but it warned that "widespread food shortages are inevitable," unless the security situation improves soon.

The United States and the Dominican Republic, which shares the island of Hispaniola with Haiti, feared a surge of Haitian refugees.

The Dominican Republic sent 1,500 extra troops to double the number patrolling its 225-mile border with Haiti, said Gen. Jose Miguel Soto Jimenez, the country's top military official.

White House spokesman Scott McClellan said U.S. planes were patrolling Haitian shores to guard against boat people. "We've not seen any indication to indicate a surge in migration at this point," he said, making clear any migrants caught would be returned home.

Aristide supporters armed themselves with old rifles and pistols and built junkpile barricades to block the road into Port-au-Prince, setting some barriers ablaze with burning tires.

Loyalists of Aristide have become more aggressive since Haiti's small and demoralized police force has fled the rebel advance, which began on Feb. 5.

Haiti has no military — it was disbanded after U.S. troops returned Aristide, Haiti's first freely elected leader, to power in 1994.

In a letter to Powell, Rep. Barbara Lee, D-Calif., accused the Bush administration of standing by while an elected government faces violent overthrow.

"People are dying, and our own commitment to democracy is under siege ... our failure to support the democratic process and help restore order looks like a covert effort to overthrow a government," Lee said.

Aristide, hugely popular when he was elected, has since lost a lot of support. Opponents accuse the former priest of failing to help those in need, condoning corruption and masterminding attacks on opponents by armed gangs. Aristide denies the charges. Flawed legislative elections in 2000 led international donors to freeze millions of dollars in aid.