PORT-AU-PRINCE, July 16 (Reuters) - Fair elections in Haiti cannot be held for at least a year after the assassination of President Jovenel Moise due to the influence of violent gangs and a compromised electoral council, a senior opposition leader said in an interview. The brazen killing of Moise last week by a suspected hit squad of foreign mercenaries has upended the impoverished Caribbean country, including its already fragile political system, which has been unable to hold elections since 2016. A referendum on a new constitution and delayed legislative and presidential elections are currently scheduled for Sept. 26. Senator Patrice Dumont, one of only 10 sitting lawmakers in the normally 30-seat Senate, said late on Thursday that quick elections are "impossible" given problems including manipulated voter lists and an electoral authority he sees as beholden to Moise"s allies and hostile to opposition parties. Dumont, who has been a staunch critic of Moise, also pointed to what he described as past deals with gangs brokered by the slain leader that effectively ceded territory to them. "Candidates can"t run campaigns under these circumstances," he said, arguing that the power of the criminal outfits must first be tamed by a revamped national police under the leadership of a new chief. "We"re talking at least one year away," Dumont said, referring to when elections could realistically be held, and suggested that it could take as long as 18 months. Moise had been ruling by decree since last year, after previously scheduled elections did not take place and the mandates of all lower house deputies and most senators expired. Dumont, who represents the country"s Ouest department, which includes the capital Port-au-Prince, also heaped criticism on acting Prime Minister Claude Joseph for clinging to his job even though he was set to vacate the position the day after the assassination. Joseph has said the constitution gives him the authority to remain in the role. On Thursday, U.S. President Joe Biden appeared to rule out sending soldiers to Haiti to help stabilize the country and protect key infrastructure despite Joseph"s calls for a deployment of U.S. troops. Dumont, a member of the Gathering of Haitian Patriots party, or RPH, dismissed Joseph"s request as a political gambit. "He wants to show that he is pro-American, he wants to show that he"s with them and that he"s working for them," the senator said, adding that he thinks most Haitians are opposed to such a military intervention. Joseph could not immediately be reached for comment. Haiti was the first country in Latin America or the Caribbean to win independence when it kicked out its former French masters in 1804. Dumont says the best hope for political stability in Haiti following the upheaval sparked by the assassination is a transitional unity council made up of as many as five national leaders, including Joseph. "We have to come to a political compromise that"s in the public interest," he said. "It"s possible, and it"s really the only way out of this catastrophe."