United Nations Secretary-General Dag Hammarskjöld attempted to meet Tshombe for negotiations in Northern Rhodesia , but on the night of 17 September his plane crashed , killing all aboard . Hammarskjöld 's untimely death , combined with an overall rise in tensions , helped rally international support for a more robust peacekeeping approach . His replacement , U Thant , was less averse to using military force in the Congo and believed that the UN should intervene in internal Congolese affairs . Thant promptly requested that the Security Council grant ONUC a stronger mandate . This came in the form of a resolution on 24 November , which maintained the goals of previous ONUC resolutions and cleared up any remaining ambiguities surrounding the role and nature of the UN 's intervention . It reaffirmed ONUC 's ability to detain and deport foreign military personnel and mercenaries with force , described Katanga 's secessionist activities as illegal , and declared the UN 's support for the central government of the Congo in its efforts to " maintain law and order and national integrity "
his plane crashed
1961 Ndola United Nations DC-6 crash
Operation Grandslam