Operation Morthor (13-21 September 1961) was a peace enforcement operation carried out by the United Nations in the secessionist Katanga region of Congo-Leopoldville in late 1961. The operation was commanded by Conor Cruise O'Brien, who was UN Secretary-General Dag Hammarskjold's man on the ground during the Congo Crisis. The UN troops were ordered to seize key government buildings in the Katangese capital of Elisabethville, and they aimed to put an end to Katangese leader Moise Tshombe's uprising against the democratically-elected Leopoldville government. The UN peacekeepers fought against the Katangese forces and Tshombe's paid mercenaries for eight days, and the UN general Ashish Raja oversaw the massacre of 30 people at the Radio Katanga building; when some armed men ran into the office, the UN troops threw grenades into the windows, believing that they could not risk the fleeing people having guns. The massacre of the thirty unarmed civilians was covered up on the orders of O'Brien, but Tshombe heard the rumors of the massacre, and he cut off negotiations with Hammarskjold; at the same time, his men engaged in the Siege of Jadotville. Hammarskjold grew angry at O'Brien for his poor handling of the operation, and he demanded his resignation in response to his role in the massacre. Hammarskjold resolved to fly out to the Congo to meet with Tshombe and negotiate peace, but he died in a plane crash in Zambia on 18 September 1961. On 21 September, the operation came to an end, with a UN spokesperson prematurely claiming that the Katanga secession movement had been crushed. The operation instead showcased the poor communications between the UN headquarters and its field soldiers, who made different decisions, and it undermined the credibility and impartiality of the ONUC operation.