The Indians kidnapped were the captain of the ship, chief officer and a bosun.
The pirates were not detected prior to their boarding the vessel, Singapore-flagged MDPL Continental One, on June 13 some 7 nautical miles off the Offon oil field, according to a security source.
They were said to have reached the bridge from inside to the astonishment of the personnel on board but did not inflict any injuries on the inmates, just as they made away with computers and other valuables.
Early this year, two Indians, three Ukrainians and one Russian had been kidnapped in the Niger delta region by pirates who had stormed a ship they were travelling in Nigeria's oil-rich southern state of Bayelsa.
They were later released unharmed.
Kidnappers in the region often demand for ransom before the release of their captives.
Five Indians kidnapped in a similar manner in December last year were released but there was no mention of any payment of ransom.
Piracy is common in Nigeria, Africa's top oil producer, especially in the oil-rich delta region. Attackers would go for oil-laden cargo or kidnap ship crews.
