Sudan’s army chief Abdel Fattah al-Burhan struck a defiant tone on Wednesday after a drone hit an army base he was visiting in eastern Sudan, casting doubt on recent efforts to bring an end to a 15-month civil war.

A statement by the army said the attack took place at a graduation ceremony at the Gibeit army base, about 100 km (62 miles) from the army’s de facto capital Port Sudan in Sudan’s Red Sea state, and that five people were killed.

Witnesses confirmed that Burhan was at the base when the drone struck on Wednesday morning. Official sources said he remained in the area and returned to the base to speak to troops, contradicting earlier reports that he had left for Port Sudan.

An adviser to the leader of the Rapid Support Forces (RSF), the army’s rival in the war, denied that the paramilitary force was responsible for the strike.