Haitian police demanding better working conditions shot up the army headquarters on Sunday, killing two servicemen and wounding a dozen more, the Defence Ministry said, prompting the government to cancel an upcoming carnival.
In a statement issued Sunday evening, the government said it had observed "with concern and dismay that terror has reigned in certain arteries of the Port-au-Prince metropolitan area."
In order to avoid a "bloodbath... it has been decided to cancel the carnival," which was scheduled to take place Tuesday, the statement said.
Media reports had said six people were wounded in the attack in Port-au-Prince by what the ministry said were gunmen wearing masks.
"We are under siege. We are coming under fire with all kinds of weapons -- assault rifles, Molotov cocktails, tear gas," said General Jodel Lessage.
He said soldiers had returned fire but did not give an injury toll, nor could he say how many people were at the army headquarters, near the presidential palace, at the time of the attack.
The situation remained tense as night fell in the city.
For months, Haitian police have been demanding better working conditions, in particular the right to form a union so as to ensure transparency in talks with the police hierarchy.
Last week, some officers took to the street, blocking them and setting fire to cars.
On Saturday, President Jovenel Moise announced measures designed to ease the crisis, including the creation of a compensation fund for families of police who die in the line of duty and a fund to provide officers with insurance.
Haiti has witnessed a spike in kidnappings for ransom since the beginning of the year and fighting between rival crime gangs, which regularly set up roadblocks on Haitian highways.
The destitute Caribbean country has also been gripped by a political crisis for more than a year as people demand the resignation of Moise.
Since coming to power in February 2017, Moise has faced the anger of an opposition movement that refuses to recognise his victory in an election widely seen as dubious. Moise is also accused of corruption.