Four naval officers have been killed and three crew members abducted after Nigerian pirates raided a dredger.

Security consultancy Dryad Global has received reports that a firefight broke out on the 3,500-dwt Ambika (built 1979), 5.5 km from the mouth of the Ramos river on the evening of 2 January.

"After heavy exchange of fire the pirates were able to board the vessel and abducted three crew members (two Russians and one Indian), leaving behind five crew members," Dryad said.