Mali's peacekeeping mission was started in April 2013, after Tuareg separatists and Islamic militants began a rebellion in the desert north. The government and separatists signed a peace accord last year, but there is still periodic violence.
One peacekeeper was killed and three seriously wounded by rockets or mortars fired at the U.N. peacekeeping mission -- known as MINUSMA -- in Gao late on Tuesday. About 10 civilians were also injured in the attack, MINUSMA said.
In a later assault carried out with light arms on the UN antimining operation (UNMAS) in a different neighborhood of Gao, two private Malian security guards and an international expert were killed, MINUSMA said.
The nationalities of the peacekeepers, MINUSMA personnel or the international experts were not immediately clear.
MINUSMA head Mahamat Saleh Annadif called on the Malian government and the local authorities to make sure that those responsible were brought to justice.
Al Qaeda in the Islamic Maghreb said on social media that they had engaged in battle with "crusader occupation forces" in the northern Mali city of Gao on Wednesday, according to SITE Intelligence Group, a monitoring firm.
The group did not provide any specific information and said it would publish a longer statement later.
The double assault occurred just days after five UN peacekeepers were killed and one injured in an ambush on a convoy in central Mali.
Although French forces seized control of key towns following the 2013 uprising, Islamist militants remain active, claiming responsibility for attacks beyond Mali's borders.