PORT-AU-PRINCE, HAITI (REUTERS) - One of Haiti's most powerful gang leaders said on Saturday (Jul 10) that his men would take to the streets to protest the assassination of President Jovenel Moise, threatening to pitch the impoverished Caribbean country deeper into chaos.

Mr Jimmy Cherizier, a former cop known as Barbecue who heads the so-called G9 federation of nine gangs, railed against police and opposition politicians whom he accused of colluding with the "stinking bourgeoisie" to "sacrifice" Mr Moise this week.

"It was a national and international conspiracy against the Haitian people," he said in a video address, dressed in khaki military fatigues and sitting in front of a Haitian flag.

"We tell all bases to mobilise, to mobilise and take to the streets for light to be shed on the president's assassination."

Mr Moise was gunned down before dawn last Wednesday at his Port-au-Prince home by what Haitian authorities said was a unit of trained assassins comprising 26 Colombians and two Haitian Americans.

The murder and the still murky plot behind it has caused further political instability in the long-troubled country, prompting the government to call for assistance from the United States and United Nations.

Mr Cherizier said his followers would practise "legitimate violence" and that it was time for "the masters of the system" - business magnates of Syrian and Lebanese descent who dominate parts of the economy - to "give back" the country.

"It's time for Black people with kinky hair like us to own supermarkets, to have car dealerships and own banks," he said.

Some of the magnates had been at loggerheads with Mr Moise.

Fears of worsening clashes had citizens on edge in Port-au-Prince, which has been racked by violence for weeks as gang members battled police for control of streets.

"They really don't have the capacity to handle security," city resident Benoit Jean said. "There aren't enough cops."

Tension has been fanned by questions about the government's account of Mr Moise's killing, with families of at least two of the Colombians saying they had been hired as bodyguards.

Earlier on Saturday, Mr Moise's widow Martine Moise, who was wounded in the attack, accused shadowy enemies of plotting his assassination to thwart democratic change.

"They sent mercenaries to kill the president at his home with members of his family because of roads, water, electricity and the referendum as well as elections at the end of the year so that there is no transition in the country," she said.

Mr Moise had spoken of dark forces behind years of unrest - rivals and oligarchs angry about what he called his attempts to clean up government contracts and politics - and proposed a referendum to change Haiti's constitution.

The referendum, scheduled for Sept 26 along with presidential and legislative elections, could abolish the prime minister's position, reshape the legislative branch and strengthen the presidency. Critics called it a power grab.

Mr Moise's killing has clouded those plans and led to political disarray in Haiti, triggering the requests for foreign help.

The US said it has no plans to provide Haiti with military assistance for now, while the request to the UN would need Security Council authorisation.

Haitian officials have not provided a motive for the assassination or explained how the killers got past Mr Moise's security detail.

None of the president's guards were injured in the attack, Mr Mathias Pierre, the elections minister, told Reuters.

Seventeen of the men suspected of involvement in his assassination were captured after a gun battle with Haitian authorities in a suburb of Port-au-Prince, while three were killed and eight are still at large, police say.

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

Calls and e-mail messages to CTU Security were not immediately answered on Saturday. Mr Intriago could not immediately be reached for comment.

The sister of Duberney Capador, 40, a Colombian killed in the firefight with Haitian police, told Reuters in a video on Saturday that the retired soldier had been offered work in security for high-profile people.

Ms Jenny Carolina Capador said her brother messaged her on the day of Mr Moise's death, saying: "We got here too late; unfortunately the person we were going to guard...we couldn't do anything."

Colombia's foreign ministry said late on Saturday it was providing consular assistance to the detained Colombians.

The ministry posted on Twitter that it would work with Haitian authorities to repatriate the remains of the two deceased Colombians, who died in what it called "confused circumstances".

Late on Friday, the man whom Mr Moise appointed prime minister just before the assassination claimed the right to lead Haiti, pitting him against acting head of state Claude Joseph, whose government has so far managed the response to the killing.

Dr Ariel Henry, a neurosurgeon whom Mr Moise named prime minister last Monday, told Reuters it was he who held power, not interim Prime Minister Joseph, and that he was forming a government.

"After the president's assassination, I became the highest, legal and regular authority because there was a decree nominating me," he said.

Dr Henry said his government would create a new electoral council which would determine new dates for elections to be held "as soon as possible".

But he has yet to be sworn in, and Mr Joseph, who was named interim prime minister in April, has stayed put.

The power struggle has created confusion over who is the legitimate leader of the country's 11 million people.

Elections Minister Mathias Pierre said Mr Joseph would keep that role until the Sept 26 vote.

Meanwhile, Haiti's Senate, which currently comprises just a third of its usual 30 senators, nominated its head, Mr Joseph Lambert, last Friday to act as the interim president, a document reviewed by Reuters showed.