Armed men freed at least 1,300 prisoners from a jail in Beni, east Democratic Republic of Congo, in a coordinated attack in the early hours of Tuesday, the town's mayor said, blaming an Islamist militant group operating in the area.

Only 110 of the 1,456 inmates, including a number of militia fighters, remained following the simultaneous early morning assaults on the Kangbayi central prison in Beni and the military camp defending it, said Mayor Modeste Bakwanamaha.

No group immediately claimed responsibility.

"Unfortunately, the attackers, who came in large numbers, managed to break the door with electrical equipment," Bakwanamaha told Reuters by telephone. "We believe that it was the ADF who did this."

The Allied Democratic Forces (ADF), a Ugandan armed group active in east Congo since the 1990s, has killed more than 1,000 civilians since the start of 2019, according to UN figures, despite repeated military campaigns aimed at destroying it.

Two inmates were shot dead during the raid, which started at around 4:30 a.m. local time, police said on Twitter. 

A similar number of inmates escaped when the jail was attacked in June 2017.

Kangbayi prison holds a variety of militiamen including members of local defense forces and ADF fighters. Bakwanamaha said there were rumors ADF fighters in the prison were preparing a break-out in the days preceding the attack.

A year ago, the army launched a large-scale counter-insurgency campaign against the ADF. In response, the group abandoned its bases, split into smaller, more mobile groups, and retaliated against civilians.

Several attacks attributed to the ADF have also been claimed by the Islamic State, although United Nations experts have found no evidence of a direct connection between the two groups.