CAIRO — A senior Libyan security official was assassinated outside his home in the eastern city of Benghazi, officials said Wednesday. His death was the latest in a series of mysterious killings that have raised fears about the country’s precarious postwar security.

The official, Faraj Mohammed al-Drissi, who had held the post of Benghazi’s security director for only a few weeks, was shot to death late Tuesday night as he was returning from work, according to Wanis al-Sharif, a local Interior Ministry official.