GOMA, Congo (AP) — Clashes erupted Monday in eastern Congo between government troops and a rebel group believed to be backed by neighboring Rwanda, escalating to the use of mortars and rocket launchers in the first fighting between the groups since the M23 rebels overtook and later retreated from the provincial capital of Goma last year.

Fears that the rebels will try to retake Goma have been mounting ever since the United Nations Security Council created an intervention brigade with a mandate to attack the armed group. The M23 called the creation of the brigade a “declaration of war.”