"An oil servicing company was attacked by gunmen. We lost two of our men and four expatriates were abducted, one Malaysian, one Iranian," Navy spokesman Commodore Kabir Aliyu said, adding that a Thai and an Indonesian were also taken.
He said the attack took place around 33 nautical miles off the coast of Bonny, Nigeria's main oil export terminal, Reuters reports.
Netherlands-based Sea Trucks Group, whose boat Jascon was attacked, confirmed that four of its staff had been seized and that two other security guards were also wounded in the attack.
"The two remaining injured security personnel are now in Port Harcourt hospital for treatment," spokeswoman Corrie van Kessel said in a statement.
"Sea Trucks Group is making every effort to find out where the kidnappers".
Security in the Delta has improved since militant activity shut down nearly half of Nigeria's oil output around the middle of the last decade, thanks to an amnesty between various militant factions and the government.
But the situation remains volatile and inflamed by organized crime and local political rivalries.
Piracy and kidnapping in the Delta and offshore are common, and West Africa's oil-rich Gulf of Guinea is second only to the waters off Somalia for the risk of pirate attacks, which drives up shipping insurance costs.
They are seen as more of a criminal enterprise making huge sums for armed gangs than as anything political. Nigerian pirates usually release kidnapped crew members after their cargo has been looted, rather than held for ransom.
Top stories this week
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- Nautic Africa launches new RHIB
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- Nigerian army arrests 1 945, destroys ships, illegal oil refineries in 2012 crackdown
- Nigerian government to revitalise Defence Industries Corporation
- Nigeria detains two vessels in major maritime security operation
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- Nigeria arrests 15 Russian sailors carrying arms
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