Excerpts from Books and Wikipedia
"Tensions between the United States and Libya had been mounting, and a few weeks earlier a naval confrontation between Libyan and US naval forces in the Gulf of Sidra left 35 Libyan seamen dead. Two weeks later, a bomb exploded in a West Berlin discotheque frequented by US servicemen. . . . The Americans claimed to have intercepted signals proving Libyan involvement. The US air strikes were presented as a proportionate response and fully legal under Article 51 of the United Nations charter, permitting national self-defense." [Furtado: 1001 Days]