The Haitian authorities said they had killed four people who took part in the assassination of President Jovenel Moïse and arrested two others. As the threat of wider violence loomed, the U.N. Security Council was set to meet about the crisis on Thursday.

Nearly 24 hours after the assassination of President Jovenel Moïse of Haiti in the bedroom of his home, gunfire erupted in the capital, Port-au-Prince, late Wednesday as the security forces engaged in a chaotic shootout with a group they described as suspected assailants, killing four and taking two into custody.

With the country placed under a “state of siege” by interim Prime Minister Claude Joseph, he said the authorities were continuing to hunt down the “mercenaries” who carried out the attack.

“This death will not go unpunished,” Mr. Joseph said in an address to the nation on Wednesday.

But the authorities did not identify those killed or in custody, and offered no evidence of their involvement in Mr. Moïse’s death.

The rapidly evolving crisis deepened the turmoil and violence that has gripped Haiti for months, threatening to tip one of the world’s most troubled nations further into lawlessness.

Haiti’s police chief, Leon Charles, said that the security forces were in control of the situation even as he acknowledged that other suspected members of the hit squad remained at large.