YENAGOA/LAGOS, Nigeria: Nigeria’s navy said yesterday it was hunting for pirates who kidnapped four crew from a ship off the coast of the West African oil-producer at the weekend.

Pirates attacked a supply vessel off Nigeria and kidnapped four sailors in the latest such incident off the country’s oil-producing southern coast, the International Maritime Bureau said yesterday.

"Pirates armed with guns attacked, boarded an offshore supply vessel ... and kidnapped four crew members," the IMB’s Piracy Reporting Centre said of the Sunday attack.

There were "no injuries to crew members and (the) vessel continued passage to a safe port," it said.

The attack occurred some 40 nautical miles off of Nigeria’s Bayelsa state, the IMB said. It provided no further details on the nationality of the crew or the ship.

The ship, named by the navy as the MV Asso Ventuno, was boarded on Sunday about 40 miles (65 km) off the coast of Nigeria’s oil-producing Bayelsa state, according to the International Maritime Bureau (IMB).

There were no injuries to other crew members and the pirates released the ship, which continued to a safe port, IMB said. A spokesman for Nigeria’s navy confirmed the incident: "Five vessels have been deployed for patrol duties off Brass Area.

"The Nigerian Navy in collaboration with other agencies have intensified search and rescue efforts of the four kidnapped crew members of MV Asso Ventuno and apprehension of the pirates."

Piracy and kidnapping in Nigeria’s oil-producing Delta and offshore are common and the oil-rich Gulf of Guinea is second only to the waters off Somalia for the risk of pirate attacks, which drives up costs for oil and shipping firms.

Such kidnappings occur regularly off Nigeria’s oil-producing Niger Delta region, with hostages typically released after payment of a ransom.

There has been a string of kidnappings in Nigerian waters and in the restive oil-producing Niger Delta this month. Last week, pirates looted an oil tanker off Nigeria and abducted five crew, the ship’s operator said.

A 2009 amnesty deal led to a sharp drop in unrest in the region, but criminality remains widespread.

On Dec. 17, four workers from South Korea’s Hyundai Heavy Industries and a Nigerian were abducted by armed men while working at a construction site in Bayelsa. The five were freed unharmed on Friday night.

On the same day, well-armed pirates stormed and ransacked an oil tanker off the Niger Delta and kidnapped five Indian crew members.

Nigerian criminal gangs operating in the Niger Delta usually free captives after a ransom is paid.

Gunmen abducted two Lebanese men working for Nigerian construction company Setraco in Delta state this month, and killed a soldier protecting them. They are still missing.

The 83-year-old mother of Finance Minister Ngozi Okonjo-Iweala was kidnapped on Dec. 9 in Delta state but freed five days later after a military search.

In the north of Nigeria, where militants operate, another form of kidnapping of foreigners has emerged this year.

A Nigerian group said on Sunday it was behind the kidnap of a French national last week, citing France’s ban on full-face veils and its support for military action in Mali.

Western governments are increasingly concerned that militants in northern Nigeria are linking up with outside groups, including Al-Qaeda’s north African wing.