Dozens of people have been killed in a car bombing at a military camp in the northern city of Gao in Mali.

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

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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Sadou Maiga, a doctor at Gao's hospital, told Associated Press news agency that all other hospital activities had ceased with dozens of wounded victims arriving.

"Some have died from their wounds, and others are in a very grave state," he said.

"At this point, it's not the toll of dead and injured that interests me, it's saving who I can."

The provisional toll is "47 dead and several injured", according to state TV broadcaster ORTM.

Earlier, a hospital source in Gao said at least 40 people had died and 60 were hurt.

Abdoulaye Idrissa Maiga, Mali's defence minister, was to fly to the city later on Wednesday.

AQIM claims blast

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 spokesperson, said the attacker's vehicle bore the logo of the unit coordinating the joint patrols.

The suicide bomber "succeeded in tricking soldiers' vigilance" and penetrated the camp, said Kone.

Later on Wednesday, al-Qaeda's affiliate in North Africa, AQIM, claimed responsibility for the bombing, according to the SITE Intel monitoring group, saying it killed nearly 80 Malian soldiers.

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

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

France sent troops to Mali at the request of the government there in early 2013 to prevent an advance by armed groups on the capital Bamako.

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.

Security Council meeting

The UN Security Council on Wednesday agreed to consider setting up a sanctions regime for Mali to punish those who are hindering the 2015 peace agreement, according to the council's president this month.

Olof Skoog, Sweden's ambassador to the UN, said council members condemned the Gao attack, noting that "persistent delays threaten the viability of the agreement".

Despite last year's peace deal between Mali's government and secular armed groups, fighters pledging allegiance to both al-Qaeda and the Islamic State of Iraq and the Levant (ISIL) group have launched dozens of attacks on Western targets in recent months.

In December, a female French aid worker was kidnapped in Gao.

Speaking to Al Jazeera from Washington DC, Corinne Dufka, Human Rights Watch's associate director, said Wednesday's attack "was very bad news for Mali and for the international community who have put a tremendous effort in trying to put Mali back together after the spectacular collapse in 2012".

She cited the main points outlined in the HRW's latest report on human-rights abuses in Mali.

"There has been a continuing growing presence of armed groups in northern Mali and central Mali, where I documented 27 executions by armed groups of those accused of being informants for the government," she said.

"We also talk about the ongoing concerns of abuses of the Mali security forces. They have improved over the past years, but nevertheless these abuses create support for the Islamist groups that use it as a rationale to recruit.

"There have also been abuses by peacekeepers whose mandate is to ensure civilian protection."