Port-au-Prince, Haiti ? Haiti’s interim president took the reins of his country’s shattered government Monday as supporters of Jean-Bertrand Aristide demanded the ousted leader’s return.

U.S. Marines acknowledged they killed one of seven people gunned down in weekend violence — the first armed action of their week-old mission here.

Military helicopters circled overhead and U.S. Marines in armored cars patrolled the streets Monday outside the National Palace as Boniface Alexandre, the former Supreme Court chief justice, was formally installed.

“Aristide or death!” Aristide supporters yelled at the gates of the palace during the ceremony, their shouts carrying into the room where Alexandre urged his countrymen to remain calm.

“We are all brothers and sisters,” said Alexandre, who has served as president for a week and was officially sworn in Feb. 29. “We are all in the same boat, and if it sinks, it sinks with all of us.”

In the Central African Republic, meanwhile, a defiant Aristide insisted that he was still Haiti’s president and reiterated his allegation, denied by the United States, that he was forced to flee Feb. 29.

“I am and I remain the elected president,” Aristide told reporters in Bangui. “I plead for the restoration of democracy. … We appeal for a peaceful resistance.”

Washington dismissed Aristide’s declaration.

“If Mr. Aristide really wants to serve his country, he really has to, we think, let his nation get on with the future and not try to stir up the past again,” State Department spokesman Richard Boucher said.