An oil tanker hijacked in the Gulf of Guinea has been spotted off the coast of Nigeria and the 24 Russian crew members on board are believed to be safe.

The vessel's Greek-based operator, Golden Energy Management, said Wednesday that pirates still have control of the tanker.

The hijackers seized the Greek-owned Energy Centurion off the coast of Togo on Tuesday. It was anchored about 27 kilometers from the capital, Lome, when the pirates attacked.

A Togo naval ship responded to a distress call and exchanged fire with the pirates, but the attackers managed to gain control of the tanker and set sail.

The operator said it is in contact with what it called “relevant authorities” and believes the pirates' goal is to steal the oil cargo.

Piracy has become a growing problem in the Gulf of Guinea, though not of the same proportions as it was for several years off the coast of Somalia.

The International Maritime Bureau says pirates in the Gulf of Guinea usually release hostages after seizing cargo. By contrast, Somali pirates typically hold hostages for ransom.