Six foreign sailors, including two Indians, kidnapped from an oil service ship off Nigeria were released unharmed by armed pirates on Tuesday, police said.

The sailors have been kidnapped 40 nautical miles off oil-rich southern Nigeria on February 17. No ransom was paid before the security agencies regained freedom of the sailors, police commissioner for the state of Bayelsa Kingsley Omire said without giving further details.

The pirate had kidnapped the six sailors, also including Ukrainians and Russians, after storming oil service ship Armada Tuah in southern Nigeria and demanded a ransom of $1.3 million, officials said.

Last month, five Indians kidnapped in a similar manner in December were released but no mention was made of any ransom payment.

Piracy is common in Nigeria especially in the oil-rich Delta region. Attackers would go for oil-laden cargo or kidnap ship crews for ransom.

Nigeria is Africa's top oil producer.