GAO - A suicide bombing targeting militia groups committed to restoring peace in Mali left nearly 50 people dead Wednesday and struck a fresh blow at long-running efforts to stabilise the troubled north.

The car bomb attack in Gao, the region's biggest city, targeted a camp grouping former rebels and pro-government militia who are signatories to a 2015 peace accord struck with the government.

The attack occurred as former rebels from the Tuareg-led CMA movement prepared to go on a joint patrol with pro-government militia members, under the terms of the peace deal.

Mali's north fell under the control of Tuareg-led rebels and militant groups linked to Al-Qaeda in 2012. The Islamists sidelined the rebels to take sole control.

Although they were largely ousted by a French-led military operation in January 2013, implementation of the peace accord has been piecemeal with insurgents still active across large parts of the region.

The joint patrols, which also include regular Malian army troops, are supposed to help prepare for the reorganisation of the army.

President Ibrahim Boubacar Keita ordered three days of national mourning following the attack, the worst in the country in recent years. Defence Minister Abdoulaye Idrissa Maiga was to fly to Gao later Wednesday.

The provisional toll is "47 dead and several injured", said state TV broadcaster ORTM. Earlier, a hospital source in Gao said at least 40 people had died and 60 were hurt. The UN peacekeeping mission MINUSMA said dozens had died and many more were hurt.

"The explosion caused heavy losses. According to preliminary information, dozens of deaths and dozens of injuries are reported among the 600 individuals hosted in the camp," a statement said.

The attack took place at 8:40 am (GMT) as the former rival groups "were due to soon leave on a joint patrol," a MINUSMA source added.

The powerful blast, which went off during a training session, ripped apart bodies, scattering limbs across the camp, a witness said.

The vehicle used in the blast bore the logo of the unit coordinating the joint patrols, army spokesman Diarran Kone told AFP.

The assailant "came to town alone to procure equipment and fit the vehicle out to commit a suicide attack," a Malian security source who asked not to be named told AFP.

There was no immediate claim of responsibility but the camp is very close to Gao airport, a key transport hub which was closed briefly in late November following an attack blamed on militants.

The car bomb destroyed prefabricated hangars used by MINUSMA's aircraft and damage to the installations and debris on the runway made the airport temporarily unusable.

"The joint patrols were the target," French Foreign Minister Jean-Marc Ayrault told French media on Wednesday. "The political aim is to hamper the peace process and reconciliation." "Peace remains fragile," he added.

France is considering a UN Security Council draft resolution that would set up a sanctions regime for Mali to target opponents of the peace deal signed 19 months ago.

The Security Council will meet Wednesday to discuss the situation in Mali.

The proposed sanctions regime would set up a mechanism to allow individuals and entities to be blacklisted by the United Nations. Targeted sanctions include a global travel ban and an assets freeze.

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