Kidnappers have freed seven sailors, including six Russians and an Estonian, who were abducted last month from a ship off the coast of Nigeria.

French company Bourbon, which owns the ship, said Thursday the crew members are in good condition and would leave Nigeria in a few days after undergoing medical tests.

The company did not say if any ransom had been paid to release them.

The sailors were abducted October 15 near Nigeria's Niger Delta region. Nine other crew members made it safely to port.

Pirate attacks are the rise in the Gulf of Guinea, which now rivals Somalia as Africa's most dangerous waters for shipping.

The International Maritime Bureau warns ships to be careful off the coasts of Nigeria, Benin, Togo and Ivory Coast.