Military officers say Nigerian separatists have hijacked a merchant ship and threaten to blow it up with its foreign crew if authorities do not release a detained leader agitating for a breakaway state of Biafra.

Defense spokesman Maj. Gen. Rabe Abubakar says the hijacking occurred on Friday, but did not tell reporters the name of the ship. Other officers say the navy is in pursuit.

There are indications the separatists in the southeast are working with some Niger Delta oil militants in southern Nigeria, escalating conflict in a country already burdened by a deadly northeastern uprising by Boko Haram.

Secret police on Oct. 17 detained Biafran separatist Nnamdi Kanu, accusing him of terrorism. His cause sparked a 1960s civil war that killed a million people.