Dozens of al Qaeda militants reclaimed the town of Azzan in Yemen’s Shabwa province on Monday, residents said, exploiting a security vacuum in the country’s south as a civil war rages.

Azzan is a major commercial hub of about 70,000 people in an arid and mountainous region and was controlled by al Qaeda for around a year until the group was ejected in 2012 by an alliance of tribesmen and armed residents loyal to Yemen’s since ousted central government.

‘Dozens of al Qaeda gunmen arrived in the early hours of the morning and set up checkpoints at the entrances to the town and in its streets. They planted their black flag on government buildings,’ one resident who declined to be named told Reuters by telephone.

‘They faced no resistance or clashes,’ the resident said, adding that tribal militia forces quit the area as it was being taken over.

Al Qaeda in the Arabian Peninsula (AQAP) has expanded during Yemen’s civil war, which triggered a military intervention by a Gulf Arab coalition last March, and also controls the major port of Mukalla in a neighbouring province.

Sunni Muslim AQAP is viewed by Western analysts as the most dangerous arm of the global militant organisation, and claimed responsibility for the deadly January 2015 attack in Paris on the satirical French magazine Charlie Hebdo.

It has made its advances in Yemen as the Saudi-led coalition forces, which back the ousted government, have clashed with the country’s ascendant Houthi movement, which they fear is a proxy for Shi’ite Muslim Iran. The Houthis and Iran deny this.

Al Qaeda views the group, hailing from the Zaydi branch of Shi’ite Islam, as apostates.

AQAP has suffered setbacks, losing its leader and several top officials to U.S. drone strikes, and is also facing competition from the new Yemen branch of the ultra-violent Islamic State group.