At least five UN peacekeepers were killed on Friday morning when suspected Islamic militants fired rockets at a military camp.
The attack, in which 30 people were injured, took place in the town of Kidal, a military source told dpa.
Witnesses said a UN helicopter had also been hit by a missile.
Olivier Salagado, a spokesman for the UN peacekeeping mission in Mali (MINUSMA), confirmed the attack, but gave no further details.
UN Secretary General Ban Ki-moon condemned "the complex attack," his spokesman Stephane Dujarric said, noting that targeting peacekeepers was a war crime.
"The secretary general reiterates that attacks against MINUSMA will not weaken the determination of the United Nations to support the Malian government, the parties to the peace agreement, and the people of Mali, in their efforts to achieve lasting peace and stability," Dujarric said.
Kidal is about 350 kilometers north-east of Gao, where around 400 German soldiers are to be stationed as part of a UN peacekeeping mission.
On Thursday, two civilians and a customs agent were killed when gunmen fired at a customs service office in the town of Hombori in central Mali.
In 2012, northern Mali temporarily fell into the hands of Islamist fighters, who were pushed back after the intervention of the country's former colonial power France.
Germany's President Joachim Gauck was expected to speak in Mali's capital Bamako on Friday.