President Jovenel Moïse’s widow has accused the Haitian leader’s domestic opponents of organising his assassination, as prosecutors summoned leading business and political figures for questioning in connection with the killing.

Martine Moïse, who was seriously wounded in the attack last week, spoke from Florida, where she is receiving hospital treatment.

“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 in an audio message in Creole posted on her Twitter account on Saturday.

Detectives are interrogating members of the presidential security team, who were unhurt when a squad of 28 mostly Colombian mercenaries burst into Moïse’s private residence on the outskirts of Port-au-Prince in the early hours of Wednesday morning and fired 12 bullets into the 53-year-old leader.

The murder has threatened to plunge Haiti, the poorest nation in the Americas, into chaos as politicians, wealthy business leaders and powerful gang bosses vie for power amid spiralling violence and dire food and fuel shortages.

Interim prime minister Claude Joseph has tried to assert control, appealing so far without success for UN and US troops to help guard key installations. Opposition politicians on Friday named their own transitional leader, Senate president Joseph Lambert, and told the interim premier to step aside, arguing he had no legitimacy.

Jacky Lumarque, rector of Haiti’s Quisqueya university and a former consultant for the World Bank, said the country needed a genuine dialogue with civil society, “not plots by political parties”, to find a way forward.

Confusion has reigned since Moïse’s death over how to choose a temporary leader. Following a contested amendment in 2012, two different versions of the constitution offer rival formulas. The head of the Supreme Court, a possible successor, died of coronavirus last month, and only 10 elected officials remain in the country, all senators, after the mandates of all mayors and most parliamentarians expired last year without fresh elections being held.

Echoing a view widely held in Haiti, Lumarque said that trying to hold elections in September or October, as the US has urged, was “completely crazy”. The security situation did not allow for a campaign, many electors lacked the necessary voting cards and the electoral council needed replacing, he added.

International powers are wary of deeper involvement in Haiti, which has struggled to find stability after decades of political turbulence and repeated natural disasters. The Caribbean island of 11m people is heavily dependent on remittances from Haitian expatriates and international aid.

The Pentagon said on Sunday that a team of US security and law enforcement experts was travelling to Haiti to help investigate Moïse’s assassination. President Joe Biden will be briefed by the team when it returns and then decide next steps.

Bed-Ford Claude, the public prosecutor in Port-au-Prince, ordered five prominent Haitians to appear on Monday morning for questioning in connection with the killing, the newspaper Le Nouvelliste reported. They included Reginald Boulos, an opposition leader and business figure, and Steven Benoit, a former senator and presidential candidate.

Boulos gave an interview on Wednesday condemning the assassination and denying responsibility, saying: “I don’t feel the opposition today would have the capability to pull out such a well-organised mission.”

Moïse claimed before his death that he was fighting political rivals and local business tycoons angry at his attempts to clean up government contracts. However, the late president had himself been accused of corruption, allegedly skimming off millions from a subsidised Venezuelan oil scheme, and of close links to the country’s powerful criminal gangs. He denied the allegations.

Fears are now growing that the gangs will increase their control of the streets in the absence of a functioning government.

Former police officer Jimmy “Barbecue” Cherizier, one of the country’s most powerful gang bosses, has accused police and opposition politicians of colluding with the “stinking bourgeoisie” to kill Moïse and called for “legitimate violence” to force local tycoons to give back the country.

Cherizier was sanctioned by the US Treasury last year for allegedly masterminding a 2018 shantytown massacre in which at least 71 people were killed and more than 400 homes destroyed. Victims’ bodies were dragged through the streets, burnt, dismembered and fed to animals, the Treasury said.

“It was a national and international conspiracy against the Haitian people,” Cherizier said in a video address on Saturday, 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.”