Police chief Leon Charles said officers shot four people over the assassination of President Jovenel Moïse in his home on Wednesday. In a televised briefing, the chief said: “The police is still in combat with the assailants. They will be killed or captured.”
Mr Charles said three officers held hostage by the suspected gunmen were freed late.
Interim prime minister Claude Joseph said the police and military were in control of security.
In a televised national address, Mr Joseph declared a state of emergency across the country, and made a call for calm.
He said: “The situation is under control.”
Bocchit Edmond, the Haitian ambassador to the US, said the attack on the 53-year-old President Moïse “was carried out by foreign mercenaries and professional killers — well-orchestrated’.
Mr Edmond added 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 counternarcotics programs, according to the US Embassy.
Joe Biden said of the incident in a written statement: “We condemn this heinous act, and I am sending my sincere wishes for first lady Moïse’s recovery.
“The United States offers condolences to the people of Haiti, and we stand ready to assist as we continue to work for a safe and secure Haiti.”