Taliban fighters entered the Afghan army’s regional headquarters for the north hidden in military vehicles on Friday and went on a shooting spree that killed more than 100 people, Afghan and U.S. officials said Saturday, in the latest sign of an emboldened insurgency that threatens the central government.

The attack involved at least eight Taliban militants who caught the soldiers off-guard during Friday prayers, when many were unarmed in a mosque on the base or having lunch at a nearby dining facility.