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 spoke on Monday. Other officers on Tuesday told The Associated Press that the navy is in pursuit of the captured vessel.

The officers, who spoke on condition of anonymity because the issue is sensitive, said the hijackers have given the government 31 days to free Kanu or say they will blow up the ship along with its crew.

Maritime industry reports indicated the vessel was an oil tanker seized about 100 miles (160km) off Nigeria’s Bakassi Peninsula.

“The group boarded the tanker from two fast boats and took control over the vessel and locked the crew in the mess room before heading for the Niger Delta", the Bulgarian-based Maritime News reported.

In an apparently unrelated development, pirates seized the Greek-owned 9,055-dwt chemical tanker Leon Dias (built 2003) off Nigeria’s coast, according to an official of the Nigerian Maritime Administration and Safety Agency who insisted on anonymity because he is not authorised to speak to reporters.

He said it was hijacked on Friday, other reports said Sunday, and diverted to an oil terminal off Cotonou, capital of neighboring Benin. Maritime News said the chief officer was seriously injured and is being held hostage with four other seamen.

The ultimatum from the separatists was given at the weekend by “General Ben.” Ben is not a separatist but “some Niger Delta militants have shown interest in working with us,” said Uchena Madu, a leader of the Movement for the Actualization of a Sovereign State of Biafra.

Officials at Leon Shipping & Trading were said to be all in a meeting and couldn’t immediately respond to TradeWinds’ request for comment

The hijacking indicates the separatists could be working with some Niger Delta oil militants blamed for recent bombings of pipelines in the oil-rich south, escalating conflict in a country already burdened by Boko Haram’s deadly Islamic uprising in the northeast and violent ethno-religious confrontations between farmers and herders in central Nigeria.

Africa’s biggest economy and oil producer is also being battered by slashed petroleum prices.

Secret police on 17 October detained Nnamdi Kanu, director of banned Radio Biafra, and since have accused him of terrorism, sparking protests in which police are accused of killing several demonstrators.

Nigeria’s Igbo people prosecuted a civil war to create a separate state of Biafra in the southeast that killed a million people in the 1960s. Many Igbos claim they still suffer discrimination.