Washington, Nov. 11 -- A commander of an Iranian terrorist proxy group allegedly helped orchestrate a failed attack on a British Air Force base housing US bombers - using coded messages relayed through family members while sitting in a federal jail in New York, according to a new US indictment.

Mohammad Baqer Saad Dawood Al-Saadi, an alleged commander associated with Iran-backed Kataib Hezbollah, is accused of coordinating the September plot to attack RAF Fairford in southwest England, where US B-1 bombers were stationed. Prosecutors allege that he communicated instructions through intermediaries, even after being arrested and placed in custody in the United States.

The eight-count superseding indictment, made public on Tuesday, names two...