Twenty-five more were wounded in the attack that happened early on Sunday at the Aguelhok base 200 kilometres north of Kidal and towards the border with Algeria.
Ten peacekeepers from Chad were killed and at least 25 were injured Sunday in an attack on their camp near a village in northern Mali, UN Secretary-General Antonio Guterres said.
Nusrat Al Islam, an Al Qaeda affiliate, claimed responsibility for the attack in a statement.
Guterres strongly condemned what he described as a "complex attack" on the UN peace mission's camp in Aguelhok, near Kidal.
The identity of the attackers was not immediately clear. UN peacekeeping and French forces are stationed in northern Mali to combat well-armed militant groups seen as the gravest threat to 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 earlier.
The mission's chief Mahamat Saleh Annadif demanded "a robust, swift and concerted response."
A 2015 peace deal signed by Mali’s government and separatist groups has failed to end the violence. Militants 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.