The Cite Soleil slum, one of the most poverty-stricken areas in Haiti, is run by warring gangs and so overcrowded that some residents sleep in shifts.
It was not clear whether those killed were gang members or civilians caught in the cross fire.
"We were conducting an operation to take over a building used by the bandits to launch attacks at our troops," Elamarti said.
Another person wounded in the same incident died that day in a hospital operated by the humanitarian organisation Medecins Sans Frontieres (Doctors Without Borders), according to a hospital spokesman.
UN officials said they have been instructed to intervene in other slums considered hotbeds of violence and crime, such as Martissant, south of the capital, where a freelance photojournalist, Jean Remy Badiau, was shot dead last week.
Badiau was killed because he took pictures of gang members who have been fighting for control of the slum, according to his wife.
The UN force has been in Haiti since shortly after the former president, Jean-Bertrand Aristide, was ousted in an armed rebellion in February 2004.
Politically motivated violence appears to have receded since the election Rene Preval, highly popular among the country's poor, as president almost a year ago.
But poverty, joblessness and the drug trade continue to fuel widespread crime.