A squad of gunmen assassinated Haitian President Jovenel Moise and wounded his wife, with four suspects later shot dead by police.
Three police officers held hostage by the suspected gunmen were freed late on Wednesday, said Leon Charles, chief of Haiti’s National Police, while two arrests were made.
The killing of Mr Moise threatened more turbulence for a country already enduring gang violence, soaring inflation and protests of his increasingly authoritarian rule.
Interim prime minister Claude Joseph said the police and military were in control of security in Haiti, the poorest country in the Americas where a history of dictatorship and political upheaval have long stymied the consolidation of democratic rule.
In an interview with The Associated Press, Mr Joseph called for an international investigation into the assassination, said that elections scheduled for later this year should be held and pledged to work with Mr Moise’s allies and opponents alike.
He said: “We need every single one to move the country forward”.
He also alluded to enemies of the president, describing him as “a man of courage” who had opposed “some oligarchs in the country, and we believe those things are not without consequences”.
Despite Mr Joseph’s assurances that order would prevail, there was confusion about who should take control and widespread anxiety among Haitians.
Authorities declared a “state of siege” in the country and closed the international airport.
The normally bustling streets of the capital, Port-au-Prince, were empty on Wednesday.
Sporadic gunshots were heard in the distance, public transportation was scarce, and some people searched for businesses that were open for food and water.
Bocchit Edmond, the Haitian ambassador to the United States, said the attack on the 53-year-old Mr Moise “was carried out by foreign mercenaries and professional killers – well-orchestrated”, and that they were masquerading as agents of the US Drug Enforcement Administration.
The DEA has an office in the Haitian capital to assist the government in counter-narcotics programmes, according to the US Embassy.
Mr Joseph said the heavily armed gunmen spoke Spanish or English, but gave no further details.
Mr Moise’s wife, Martine, was in stable but critical condition and was being moved to Miami for treatment, Mr Edmond said in Washington.
Haiti has asked the US government for assistance with the investigation, he said, adding that the assassins could have escaped over the land border to the Dominican Republic or by sea.
The Dominican Republic said it was closing the border and reinforcing security in the area, describing the frontier as “completely calm”.