PORT-AU-PRINCE, Haiti — With foreign powers weighing in, Haitian officials announced a new prime minister on Monday, in an attempt to resolve a caustic leadership struggle in the wake of President Jovenel Moïse’s assassination.

Claude Joseph, the prime minister who took control of Haiti’s government immediately after the killing, said he was stepping down in favor of Ariel Henry, a neurosurgeon who had been appointed to the position by the president shortly before he was killed.

“I’m a courageous man, I took charge, and I spoke to the population and said, ‘Keep calm. We need to behave intelligently,’” Mr. Joseph said in an interview, speaking of the role he played after the president’s death. “Otherwise, no one knows what would have happened.”