Gunmen ambushed a Malian army convoy in central Mali on Thursday, killing at least 15 soldiers, the army said, just days after another attack in the country’s north left several dozen civilians dead.

The soldiers had been heading from the town of Douentza to Boni when it came under attack by a vehicle that exploded as it passed, the Malian military announced. Intense gunfire soon followed, the statement said.

The attack has not been claimed, but bears the mark of armed groups linked to al- Qaeda that have been active in the region for years. Islamic extremists grabbed control of major towns across northern Mali in 2012.

A French-led military operation the following year dispersed the militants, but they have mounted frequent attacks against Malian soldiers and U.N. peacekeepers in the years since. Islamic extremists have also made inroads into central Mali, destabilizing the region.

France, the former colonial power, has announced it will withdraw more than 2,000 troops from its anti-extremism force in Africa’s Sahel region by early next year.

Islamic militants, though, have continued to launch devastating attacks, and hundreds of civilians have died this year in a series of massacres targeting villages along Mali’s border with Niger.