At least five people have been killed in clashes between UN troops and armed gang members in a Haitian shantytown near the capital, Port-au-Prince.
Opposition to the UN peacekeepers is growing amongst slum dwellers
The UN mission said the confrontation began early on Friday morning, but were unable to comment on casualty figures.
They said a UN vehicle was also burnt in the clashes at the Cite Soleil slum.
UN peacekeepers - in Haiti since 2004 - have stepped up patrols amid worsening security in the area, but opposition to their presence has grown.
They were sent to maintain order after a revolt ousted the former President, Jean-Bertrand Aristide.
A UN statement said its troops had launched a joint operation with Haitian police as part of an effort to fight a recent upsurge in kidnapping and other violence by gangs based in the slum.
Eyewitnesses said several victims were taken to hospital, and local residents showed reporters the bodies of five men who, they said, were killed by UN fire.
Residents had previously accused UN soldiers of firing indiscriminately during gun battles with gang members.
The UN has denied this, saying peacekeepers only open fire when they come under attack.
The Brazilian-led UN force includes more than 8,000 soldiers and police supported by some 1,000 civilian personnel.