The death toll from Wednesday's bomb attack on a military camp in northern Mali has risen to 77, a French army spokesman said.

The area hit by the blast houses government soldiers and armed groups who conduct mixed patrols under a UN-brokered peace deal aimed at curbing violence in the region.

"We regret to say that there are 77 deaths," said Colonel Patrik Steiger, speaking to reporters in Paris.

France intervened in Mali in 2013 to drive back groups that got control of large swaths of the country a year earlier, and it maintains a large, regional operation.

Wednesday morning's explosion hit the Joint Operational Mechanism base in Gao, which was seized by armed groups in 2012 before French forces drove them out a year later.

Specifically, former rebels from the Tuareg-led CMA movement were preparing to go on a joint patrol with pro-government militia members, under the terms of the 2015 agreement, when the attacker struck.

President Ibrahim Boubacar Keita declared a three-day mourning period following the attack, the worst in years.

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Witnesses said the car bearing explosives breached the camp at around 9am, just as hundreds of fighters were gathering for a meeting.

Diarran Kone, a Mali army spokesman, said the attacker's vehicle bore the logo of the unit coordinating the joint patrols.

AQIM claims blast

Later on Wednesday, al-Qaeda's affiliate in North Africa, AQIM, claimed responsibility for the bombing, according to the SITE Intel monitoring group.

AQIM described the attack on the Joint Operational Mechanism base as "punishment for cooperation with France".

The incident occurred days after Francois Hollande, the French president, visited the camp.

Gao is considered the best-secured town in northern Mali, with multiple UN, French and Malian army checkpoints along main roads.

However, the offices of the UN peacekeeping mission located next to the airport terminal were razed by a truck-bomb explosion last month.

The UN has deployed 13,000 troops in Mali to serve in the MINUSMA force, considered one of the deadliest missions in peacekeeping.