Nigerian oil industry sources say gunmen have attacked a vessel in the oil-rich Niger Delta region, killing one crewmember and injuring another.

Details of the incident are not clear, but the sources say the attack targeted a boat operated by U.S. oil giant ExxonMobil.

Attacks and kidnappings have become common in the Niger Delta over the past two years, and they have cut Nigeria's oil production by about 20 percent.

Last month, attackers with the rebel Movement for the Emancipation of the Niger Delta claimed responsibility for blowing up a major oil pipeline belonging to Royal Dutch Shell.  The group said in a statement that it aims to ultimately cripple Nigeria's oil industry. 

The militants have said they want local villages to get a greater share of the region's oil wealth. 

Violence in the Niger Delta has declined in recent months, as the government of President Umaru Yar'Adua tries to negotiate a cease-fire.

Nigeria remains Africa's largest oil producer, pumping more than two million barrels per day.

Some information for this report was provided by AP and Reuters.