A vehicle packed with explosives detonated at a camp housing soldiers and members of rival armed groups in the region's main city, Gao.
Mali's northern desert region has been restive since it was captured by militant Islamists in late 2012.
Despite French military intervention in 2013, the region remains tense.
Al-Qaeda in the Islamic Maghreb (AQIM) said the suicide bombing was meant to punish rebel groups co-operating with France, according to a statement obtained by the SITE Intelligence Group.
AQIM said a group called al-Mourabitoun was responsible and named the bomber it said carried out the attack. Malian media had earlier suggested several bombers took part.
The victims were involved in conducting patrols in this highly volatile area under a deal backed by the UN in a bid to stop the violence there.
The accord between the government and rebel groups was signed in June 2015.
Al-Mourabitoun also said it was behind the hostage-taking at the Radisson Blu hotel in the Malian capital, Bamako, in November 2015, and a deadly raid on the Splendid Hotel in the capital of Burkina Faso, Ouagadougou, in January 2016.
It is not the first time the military in Mali has been targeted by a deadly attack.
In July last year, about 17 soldiers were killed and 30 others wounded in an attack on a military base in the central town of Nampala.
Mali's President Ibrahim Boubacar Keita has declared three days of national mourning in a tweet following the latest attack.
The fight against extremist groups is one of the major challenges of Mr Keita's government.
But a new report by Human Rights Watch says the Malian government is not doing enough to protect civilians from the militants.
Wednesday's attack shows that even soldiers aren't safe, says the BBC World Service Africa editor James Copnall.
"If the security situation continues to deteriorate, then soon there won't be any peace to keep in Mali," UN peacekeeping chief Herve Ladsous told the UN Security Council.
Al-Qaeda's North African affiliate says a group linked to it carried out the suicide attack that killed at least 50 people in northern Mali.