Port-au-Prince, Haiti ? Haiti’s president urgently appealed for the world’s help Tuesday to avert a bloodbath and a new exodus of boat people as rebels threatened the capital. Despite last-ditch diplomacy, an opposition coalition rejected a U.S.-backed peace plan.

Supporters of President Jean-Bertrand Aristide armed with old rifles and pistols built junkpile barricades blocking the road into Port-au-Prince, setting some of the barriers ablaze with burning tires.

The opposition rejected a peace plan that would have kept Aristide as president, but with diminished powers and compelled to share government with his rivals.

The neighboring Dominican Republic sent 1,500 extra troops to patrol its border with Haiti, said military spokesman Col. Juan Julio Tejeda Madera. He said that brought to 3,000 the number of troops at the 225-mile border. He said he didn’t expect a mass influx of refugees, “but we are ready.”

At a news conference, Aristide warned that if rebels try to take the capital, the death toll would be high. So far, at least 70 people have been killed in the three-week uprising.

“Should those killers come to Port-au-Prince, you may have thousands of people who may be killed,” Aristide said, adding the rebels had taken their fight overnight to the northwest town of Port-de-Paix. “We need the presence of the international community as soon as possible.”

White House spokesman Scott McClellan said U.S. planes were patrolling Haitian shores to guard against any possible surge in boat people.

“We continue to carefully monitor that situation, but 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.

Most boat people want to go to the United State, but others go to the Bahamas or Cuba. On Monday, 32 Haitian boat people landed in Jamaica, bringing to 62 the number who have arrived there in the past 10 days.