Haitian President Jovenel Moïse has been murdered and the first lady injured in an attack on their home in Port-au-Prince.
Unidentified gunmen stormed the property at 01:00 local time, interim PM Claude Joseph said.
PM Joseph has called for calm and declared a state of emergency nationwide.
Jovenel Moïse, 53, had led Haiti, one of the poorest nations in the world, since 2017 but had faced widespread protests demanding his resignation.
Haiti’s recent history has been plagued by coups, political instability and widespread gang violence.
First Lady Martine Moïse later reportedly arrived by plane in Fort Lauderdale, south Florida, for treatment. There is no official word on her condition.
Claude Joseph called the shooting of the president a “heinous, inhuman and barbaric act”, saying the attackers were “foreigners who spoke English and Spanish”. Haiti’s official languages are Creole and French.
Some reports spoke of men dressed in black carrying high-powered weapons who may have pretended to be part of a US drug enforcement operation, although no official details have been given.
Haiti’s ambassador to the US, Bocchit Edmond, said there was “no way” US drugs agents carried out the attack. He believed it was the work of “professional mercenaries”.
Addressing the nation, PM Joseph vowed the killers would be brought to justice and said the security situation was “under control”.
The state of emergency, or “state of siege”, allows for the banning of gatherings and use of the military for police roles, along with other extensions of executive powers.
PM Joseph said that “all measures have been taken to ensure continuity” and that “democracy and the republic will win”.
But questions remain about how much control PM Joseph can assert.
Haiti’s constitution says ministers, under the leadership of the prime minister, take control in the event of presidential vacancy until elections can be called.
However, that also remains unclear, as a new prime minister, Ariel Henry, was named by Jovenel Moïse just this week but has yet to be sworn in.
The US later said it believed elections should go ahead this year, to bring about a peaceful transfer of power.
The US has been Haiti’s biggest donor for 50 years but has had a fractious relationship with some of its rulers and has carried out a number of blockades and interventions.
The country has also had strong counter-narcotics ties with Haiti to try to prevent South American drugs being shipped through the nation and on to the US.
The neighboring Dominican Republic ordered the “immediate closure” of its border with Haiti.
President Jovenel Moïse, 53, had been in power since February 2017.
His time in office was rocky as he faced accusations of corruption and there were widespread demonstrations in capital Port-au-Prince and other cities earlier this year.
Haiti’s opposition said that Jovenel Moïse’s five-year term should have ended on February 7, 2021, five years to the day since his predecessor, Michel Martelly, stepped down.
However, there had been a year’s delay to elections after Michel Martelly’s departure, and Jovenel Moïse insisted he had one more year to serve as he did not take office until February 7, 2017.
Parliamentary elections should have been held in October 2019 but disputes have delayed them, meaning Jovenel Moïse had been ruling by decree.
In February 2021, on the day the opposition wanted him to leave office, President Moïse said an attempt to kill him and overthrow the government had been foiled.
Haiti has also faced a wave of recent gang violence and kidnappings, particularly in the capital, with a number of its districts becoming no-go areas.
The worsening living standards in the nation of 11 million people have pushed nearly 60% below the poverty line.