Nigerian separatists have hijacked a merchant ship and threatened to blow it up with its foreign crew if authorities do not release a detained leader agitating for a breakaway state of Biafra, military officers said Tuesday.

Maj. Gen. Rabe Abubakar, the defense ministry spokesman, confirmed the hijacking occurred on Friday and called it “an act of sabotage.” He did not tell reporters the name of the ship.

Abubakar