Navy spokesman, Colonel Kabir Aliyu, said the boat in which the victims were traveling belonged to a Netherlands- based oil servicing company, Sea Truck Group Jascon.
The four abducted foreigners were Indonesian, Iranian, Malaysian and Thai.
Those killed and two other injured were Nigerians.
Spokesperson for the shipping company, Corrie van Kessel, confirmed that the employees for the company were kidnapped by the attackers who besieged one of the company's vessels in Nigerian waters.
The attack happened 33 nautical miles off Port Harcourt and authorities in Nigeria said they have not established the reason for the pirates action.
The area located within the oil-rich African country's Niger Delta region has been known for frequent attacks by sea pirates who either stole oil or just demanded ransom for the release of their hostages.
The region was infested with militants for years who claimed to be fighting for resource control and crippled oil production, until the Nigeria government gave them amnesty in exchange for weapons.
