BAMAKO (AFP) - A suicide bombing on Wednesday (Jan 18) on a camp grouping former rebels and pro-government militia in troubled northern Mali left 40 people dead, UN and local sources told AFP.

The president's office ordered three days of national mourning following the attack, the worst in the country in recent years.

A member of the UN peacekeeping mission MINUSMA, who asked not to be identified, initially put the death toll at 37 but hospital sources later said 40 people had been killed and 60 hurt.

The camp is located in Gao, a former bastion for Malian rebels and Islamist fighters who together seized control of much of the country's vast arid north in early 2012.

It was set up under a 2015 peace deal signed between the government and various militia and rebel groups following a French-led international military intervention that was launched in 2013 but which is still in place.

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

Implementation of the peace accord has been piecemeal with insurgents still active across large parts of the region.

"The suicide bomber came in a vehicle and blew himself up," the MINUSMA source said.

The attack took place at 8.40 am (local and GMT) as the former rival groups "were due to soon leave on a joint patrol", the source added.

The camp is close to Gao airport, a key transport hub, which was closed briefly in early December following a suicide attack blamed on militants.

Fighting broke out following the attack between armed groups, leaving at least one person dead and a dozen injured.

A car bomb destroyed prefabricated hangars used by the mission's aircraft, MINUSMA said at the time, and damage to the installations and debris on the runway made the airport temporarily unusable.