The UN mission in Mali, MINUSMA, has sent a team to the site to check for possible casualties and investigate the cause of the crash, said spokesman Farhan Haq in New York. The helicopter came down near Tabankort, south of Gao.
UN diplomats separately confirmed that the attack helicopter and the crew had been supplied by Germany to MINUSMA.
And a UN source in the northern city of Gao described a German helicopter crashing in "an accident" in the Ilouk area, adding "we will release the toll later."
That source added "nothing at this stage" would suggest the aircraft "was hit or shot at" as it monitored ongoing fighting in the area.
The United Nations operation, launched in 2013, is considered the UN's most dangerous peacekeeping mission, with dozens of its staff killed in the last four years.
Germany has reinforced its presence in Mali this year, deploying several helicopters and raising the number of Germans serving in MINUSMA to 639 as of June. France has expressed hope its European neighbour will do more in the poor and insecure Sahel region.
The crash comes two years after two Dutch UN peacekeepers died when their Apache attack helicopter crashed in northern Mali.
Northern Mali is the site of frequent clashes between rival armed groups, as well as a haven for jihadist activity.
Fighting between the Gatia pro-government group and the CMA former rebel alliance close to the city of Kidal claimed numerous victims on Wednesday, the military source within the UN mission said, separate to the clashes near Gao.
A local official accused the rebels of using "jihadist back-up" to gain an advantage over the pro-government fighters.
The groups' ongoing disputes threaten the future of a peace deal they signed in 2015 aimed at curbing northern uprisings and keeping the jihadists in check, according to the United Nations.
In 2012, key cities in Mali's north fell under the control of jihadist groups linked to Al-Qaeda, who exploited an ethnic Tuareg-led rebel uprising.
While the Islamists were largely ousted by a French-led military operation, attacks have continued on UN and French forces, civilians and the Malian army.
Former rebels still control the northern city of Kidal, and fighting between groups previously loyal to the Tuareg rebellion and pro-government militia is common, in violation of a ceasefire.
The United Nations has condemned such violations by the combatants, but the state is absent from much of Mali's northern territory and its terrain is very difficult to traverse.
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