Ten UN peacekeepers from Chad were killed and at least 25 were wounded while repelling an attack by armed assailants near a village in northern Mali on Sunday, the West African nation's UN mission and the United Nations said.
The identity of the attackers was not immediately clear.
UN peacekeeping and French forces are stationed in northern Mali to combat well-armed jihadist groups seen as threatening security across Africa’s Sahel region.
The clash near Aguelhok occurred early on Sunday following an attack by assailants in many armed vehicles, the UN peacekeeping mission in Mali (MINUSMA) said in a statement.
The United Nations said peacekeepers had thwarted the attack, but 10 died and at least 25 were wounded.
"The Secretary-General reaffirms that such acts will not diminish the resolve of the United Nations to continue supporting the people and Government of Mali in their efforts to build peace and stability in the country," it said.
A 2015 peace deal signed by Mali’s government and separatist groups has failed to end the violence.
Islamists have also staged assaults on high-profile targets in the capital, Bamako, and in neighbouring Burkina Faso and Ivory Coast.
French forces intervened in Mali in 2013 to drive back fighters who had hijacked a Tuareg uprising a year earlier, and some 4,000 French troops remain there.
The UN Security Council then deployed peacekeepers, which have been targets of a concerted guerrilla campaign.