Major General Dewan Prem Chand launched Operation Grandslam on 28 December and by the end of the day UN troops had seized downtown Élisabethville. Reinforced by recently amassed air power, United Nations peacekeepers successfully completed the first phase of the operation by the end of the year. In early January the United Nations forces turned their attention towards remaining strongholds in southern Katanga. Indian peacekeepers surpassed their orders and crossed the Lufira River ahead of schedule, generating panic behind the Katangan lines and causing an incident among United Nations leadership. Tshombe, realizing that his position was untenable, sued for peace on 15 January 1963. Two days later he signed an instrument of surrender and declared the Katangan secession to be over.