- The "alleged assassins" of Haiti's President Jovenel Moise were in custody less than 24 hours after their brazen attack.
- The country will observe two weeks of national mourning from Thursday.
- US President Joe Biden condemned the killing as "horrific" and said Washington was ready to assist in any way.
The "alleged assassins" of Haiti's President Jovenel Moise were in custody on Wednesday, a government minister said, less than 24 hours after the leader of the impoverished Caribbean nation was killed in a gun attack at his home.
"Alleged assassins of (Moise) intercepted by the National Police in Pelerin shortly before 6 pm tonight," deputy communications minister Frantz Exantus tweeted, adding that more details would be released shortly.
The attack at Moise's private residence in the capital Port-au-Prince, which also left First Lady Martine Moise wounded, pitched the crisis-hit country into uncertainty, leaving citizens fearful as shocked world leaders called for calm.
TIMELINE | Haiti: A history of political turmoil
The UN Security Council will hold an emergency meeting on Haiti around midday on Thursday, and interim Prime Minister Claude Jospeh - who is due to be replaced this week - declared a "national state of siege" granting the executive additional powers, and said he was now in charge of the country.
As international outrage spread over the killing, the airport was closed in Port-au-Prince, but witnesses said the city was quiet with the streets deserted and no extra security forces on patrol.
The attack took place around 1:00 am (0500 GMT). Joseph said the president was "assassinated at his home by foreigners who spoke English and Spanish."
"This death will not go unpunished," Joseph said in an address to the nation.
Moise's wife Martine was first treated in a local hospital before being evacuated by air ambulance to the Ryder Trauma Center in Miami.
Earlier, Haiti's ambassador to Washington, Bocchit Edmond, told reporters the killers were "professional" mercenaries who disguised themselves as US Drug Enforcement Administration agents and may have already left the country.
"We have a video and we believe that those are mercenaries," he added.
Moise had ruled Haiti, the poorest country in the Americas, by decree after legislative elections due in 2018 were delayed in the wake of disputes, including on when his own term ends.
In addition to the political chaos, kidnappings for ransom have surged in recent months, reflecting the growing influence of armed gangs in the country.
Haiti also faces chronic poverty and recurrent natural disasters.
Outside Moise's residence police and forensics experts examined bullets found in the street and searched for other evidence.
A nearby car could be seen peppered with bullet holes, its window shattered.
The capital's streets were at a standstill, with just a handful of citizens who expressed fear and disbelief.
"We didn't expect it. This is another earthquake in Haiti," said a mother of two who gave her name only as Bernadette, referring to the disaster which devastated the country in 2010.
"I can't believe it, I can't believe it," said 50-year-old Jacquelyn.
The country will observe two weeks of national mourning from Thursday.
The president had faced steep opposition from swathes of the population that deemed his mandate illegitimate, and he churned through seven prime ministers in four years.
Joseph was supposed to be replaced this week after only three months in the post.
As well as presidential, legislative and local elections, Haiti was due to have a constitutional referendum in September after it was twice postponed due to the coronavirus pandemic.
US President Joe Biden condemned the killing as "horrific" and said Washington was ready to assist in any way.
"We condemn this heinous act, and I am sending my sincere wishes for First Lady Moise's recovery," Biden said in a statement.
Washington also called for Haiti to proceed with the elections, with State Department spokesman Ned Price saying a fair vote would "facilitate a peaceful transfer of power to a newly elected president."
UN Secretary-General Antonio Guterres called on Haitians to "remain united" and "reject all violence."
European Union foreign policy chief Josep Borrell warned of "risk of instability and a spiral of violence."
Moise - a 53-year-old former entrepreneur from the north of the country - burst onto the political stage in 2017 with a message of rebuilding, campaigned on populist pledges, and was sworn in in February 2017.
The end date of his mandate became the source of a tense standoff.
Moise maintained that his term of office ran until 7 February 2022, but others claimed it ended on 7 February, 2021.
The disagreement stems from the fact that Moise was elected in a 2015 vote that was cancelled for fraud, and then re-elected in November 2016.
Without a parliament, the country fell further into crisis in 2020, and led to Moise governing by decree, fuelling growing mistrust of him.
Though the calm held in the hours after the assassination, many feared Haiti could tip further into violence.
"How much worse can hell get?" asked Haiti expert Irwin Stotzky, a professor at University of Miami law school.
"Haiti faces even more violence and death and failure as a democratic nation than ever before, which is hard to imagine given its recent and chaotic history."
The killing comes days after Moise appointed Ariel Henry, a neurosurgeon who studied in France, as Haiti's new prime minister.
Henry, 71, is close to the opposition, but his appointment was not welcomed by the majority of opposition parties, who had continued to demand the president step down.
The Dominican Republic ordered the immediate closure of its border with neighboring Haiti after the assassination.