The International Maritime Bureau is warning vessels to stay clear of waters off Nigeria after pirates killed the captain and chief engineer of a bulk carrier Monday, the third attack in West African waters in a week.

The killings off the coast of Lagos, Nigeria's largest shipping gateway, came after pirates attacked a ship and hijacked a tanker ship near neighboring Benin in the last week.

The IMB said although the average length of captivity of ships attacked off Benin and Nigeria is about 10 days compared to six months in Somali hijackings, the attacks can be more violent. While 10 attacks were reported in Nigeria in 2011, the number is "not representative of the real threat of Nigeria"

"Under reporting of attacks in Nigeria continues to be a cause for concern, and IMB states that it is aware of at least another 34 unreported incidents in Nigerian waters," the agency said.

In neighboring Benin there were 20 incidents involving tankers, eight of which were hijacked and had cargoes partly stolen.

Source: Journal of Commerce