One oil worker has been killed in an attack on a boat owned by Italian energy firm Eni's local subsidiary Agip in Nigeria's Niger Delta, while another two were reported missing.

"The boat conveying some staff of Agip was attacked by sea robbers and one of the staff of the company died when he was attempting to escape and drowned," Onyema Nwachukwu, spokesman for Nigeria's military joint task force, told Reuters on Friday.

Two other Agip staff were missing after the attack in the Tarabora creek in Bayelsa state, said Nwachukwu. One of the workers drowned after jumping into the water in an attempt to escape from the bandits.

The oil workers’ boat, the MV Terra, was reportedly ambushed by the gunmen when it was heading for the firm’s Clough Creek flow station. According to the Saturday Punch, the boat was not being escorted by security personnel when it was attacked.

Operatives of the Joint Military Task Force in the region were immediately deployed to the scene and are in search of the suspected pirates, Nwachukwu said.

A spokeswoman for Italy’s Eni said the attack occurred on Thursday. "A speed boat contracted by (Agip) was attacked and stolen," she was quoted by Agence France Press as saying, and added that there were three people on board. She said a Nigerian national who worked for the company drowned while the other two were safe.

Pirates off the coast of Nigeria tend to raid ships for cash and cargo rather than hijacking the crews for ransom like their counterparts off the coast of Somalia. However, onshore kidnapping is a major business in Nigeria, especially in oil producing coastal areas like Bayelsa.

West Africa is a worsening piracy hotspot. Attacks in the Gulf of Guinea have increased in recent months as the area, spanning a dozen countries, is a growing source of oil, cocoa and metals being shipped to the world's markets.