The group was established following the passing of Security Council Resolution 128 on 11 June 1958 in response to the 1958 Lebanon crisis, which had been triggered by an armed rebellion against the Camille Chamoun's government in May. UNOGIL was tasked with ensuring there was "no illegal infiltration of personnel or supply of arms or other materiel across Lebanese borders" following concerns from the Lebanese government about the involvement of the United Arab Republic, who they believed were, according to authors Ana Mesquita and Nigel White, "supporting the infiltration of armed elements from Syria into Lebanon" during the 1958 Lebanon crisis. In order to obtain Security Council consent amidst Cold War geopolitics, the group's mandate was deliberately narrow, limited to observation and reporting only, and it was given no authority to enforce this mandate, nor was it equipped to do so.