Suspected sea pirates on Friday attacked a vessel transporting workers for Italian firm Agip in southern Nigeria, leaving at least one person dead, the military said.

The attack that saw gunmen ambush the vessel occurred in an area of Bayelsa state in Nigeria's oil-producing Niger Delta region.

While a spokesman for a military task force in the region confirmed one Nigerian man was killed, a security source said two other people were missing. The vessel was said to have been transporting workers to an oil facility.

"The boat conveying some staff of Agip was attacked by suspected sea robbers and one of the staff of the company died when he was attempting to escape into the river and drowned," said Lieutenant Colonel Onyema Nwachukwu.

Italy's ENI is the parent company of Agip. The company did not immediately respond to a request for comment, and further details of the attack were unclear.

A 2009 amnesty deal greatly reduced unrest in the Niger Delta region, but sporadic incidents continue to occur, including robberies, piracy and kidnappings.

Nigeria is Africa's largest oil producer.