A shipping security expert says the crew of an oil tanker hijacked in Nigerian waters is from Russia, Georgia and the Philippines and that they are probably being held hostage for ransom.
Dirk Steffen of Denmark-based Risk Intelligence says claims that the Greek-owned MT Leon Dias was boarded by separatists espousing an independent state of Biafra in south-east Nigeria is most likely a cover to lend legitimacy to a kidnapping for ransom.
He says the hijackers abandoned the ship on Sunday and took five hostages with them. They include the Filipino captain and third engineer, the chief engineer and electrician from Russia and a fitter from Georgia.
Nigeria's navy said the ship is now off the coast of neighbouring Benin, guarded by that country's navy.
A man who identified himself as General Ben - similar to titles used by Niger Delta oil militants - had threatened to blow up the ship with its crew if authorities did not release Nnamdi Kanu, the director of the banned Radio Biafra detained since October 17 and accused of terrorism. The two main separatist groups have denied involvement in the hijacking.
Nigeria's government has made no comment on the hijacking, which comes amid renewed attacks on oil and gas installations in the southern Niger Delta believed to have been carried out by militants demanding a bigger share of revenue for southern states polluted by petroleum production.
Militants have threatened new attacks if the government does not fully support an amnesty programme that in 2009 halted conflict that was killing 1,000 people a year and had reduced the output of Africa's biggest oil producer by 40%.
Security forces said they have arrested some suspects in the sabotage, but did not say how many.