"Peacekeepers of the MINUSMA force at Aguelhok fought off a sophisticated attack by assailants who arrived on several armed vehicles," said Mahamat Saleh Annadif, the UN's special representative for Mali.
Eight peacekeepers have so far been confirmed dead and several others were wounded, he added in a statement.
The "cowardly" attack, he added, "illustrates the determination of the terrorists to sow chaos, Presstv reported.
"It demands a robust, immediate and concerted response from all forces to destroy the peril of terrorism in the Sahel."
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.
A 2015 peace deal signed by Mali’s government and separatist groups has failed to end the violence.
Extremists have also staged assaults on high-profile targets in the capital, Bamako, and in neighboring 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.