Haiti's interim Prime Minister Claude Joseph speaks during a news conference following the assassination of President Jovenel Moise, in Port-au-Prince, Haiti July 11, 2021. [Reuters]

Haitian police said they had arrested one of the suspected masterminds in the assassination of President Jovenel Moise on Sunday, 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 say was a unit of assassins made up of 26 Colombians and two Haitian Americans, plunging the troubled Caribbean nation into deeper turmoil.

Police said they have arrested a doctor they believe is a key suspect in organising last week's assassination of President Jovenel Moïse.

They say Christian Emmanuel Sanon, a 63-year-old Haitian national, flew into the country on a private jet in early June with "political motives", BBC reports.

Earlier on, a group of Colombians and Haitian Americans suspected of assassinating Haitian President Jovenel Moise told investigators they were there to arrest him, not kill him, the Miami Herald and a person familiar with the matter said on Sunday.

The murder and uncertainty about who hatched the plot filled the air after the assassination, which has appealed for international help.

Washington has so far rebuffed Haiti's request for troops, though a senior U.S. official said on Sunday that Washington was sending a technical team to assess the situation.

Citing people who had spoken to some of the 19 suspects detained so far, the Miami Herald said they said their mission was to arrest Moise and take him to the presidential palace.

A source close to the investigation said the 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.

Haitian police did not reply to a request for comment.

The news follows reports that some of the Colombians had said they had gone to work as security personnel in Haiti, including for Moise himself.

The Miami Herald reported the detained Colombians said they were hired to work in Haiti by Miami-based company CTU Security, run by Venezuelan emigre Antonio Enmanuel Intriago Valera.

Neither CTU nor Intriago could be reached for comment.

One phone number associated with the company in public records sent calls to an answering machine that referred to the fictional TV character Jack Bauer, who fought terrorism in the series "24."

"Thank you for calling CTU security. For Tony Intriago please leave a message or send a text. For Jack Bauer wait for the next season. Thank you for calling and have a great day."

Social media profiles that appeared to belong to Intriago included a Facebook photo showing a man in tactical gear pointing a high-powered rifle. Other photos on Instagram showed ammunition, guns, and people engaged in tactical training.

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Photos and X-ray images posted on social media at the weekend said to be from Moise's autopsy showed his body riddled with bullet holes, a fractured skull and other broken bones, underscoring the brutal nature of the attack.

Reuters could not independently confirm their authenticity.

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.

Meanwhile, one of Haiti's top gang leaders, Jimmy Cherizier, a former police officer known as Barbecue, said that his men would take to the streets to protest the assassination on Saturday.

Cherizier, boss of the so-called G9 federation of nine gangs, said police and opposition politicians had conspired with the "stinking bourgeoisie" to "sacrifice" Moise.

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