Haitian police said on Sunday they had arrested one of the suspected masterminds in the assassination of President Jovenel Moise, a Haitian man whom authorities accused of hiring mercenaries to oust and replace Moise.

Moise was shot dead early on Wednesday at his Port-au-Prince home by what Haitian authorities describe as a unit of assassins formed of 26 Colombians and two Haitian Americans, plunging the troubled Caribbean nation deeper into turmoil.

National Police Chief Leon Charles said the arrested man, 63-year-old Christian Emmanuel Sanon, flew to Haiti on a private jet in early June, accompanied by hired security guards, and wanted to take over as president.

He did not explain Sanon's motives beyond saying they were political, but added that one of those in custody had contacted him upon being arrested. Sanon, in turn, contacted two other "intellectual authors" of the assassination, Charles added.

"The mission of these attackers was initially to ensure the safety of Emmanuel Sanon, but later the mission was changed and they presented one of the attackers with an arrest warrant for the president of the republic," Charles said.

Haitian police have arrested 18 Colombians and 3 Haitian Americans, including Sanon, over the murder, Charles said. Five Colombians are still at large and three were killed, he added.

The suspected assassins told investigators they were there to arrest him, not kill him, the Miami Herald and a person familiar with the matter said earlier on Sunday.

A source close to the investigation said two Haitian Americans, James Solages and Joseph Vincent, told investigators they were translators for the Colombian commando unit that had an arrest warrant. But when they arrived, they found him dead.

Via social media, Haitians in parts of the capital Port-au-Prince were planning protests this week against the interim prime minister and acting head of state Claude Joseph.

Joseph's right to lead the country has been challenged by other senior politicians, threatening to exacerbate the turmoil engulfing the poorest country in the Americas.

Gunfire rang out overnight in the capital, which has suffered a surge in gang violence in recent months, displacing thousands and hampering economic activity.