Details about the ship, crew and cargo were unavailable, Andrew Mwangura, leader of the Kenya Seafarers Association, told CNN. The organization tracks the welfare of sailors captured by the pirates.

Mwangura said the last contact with the ship was late last week, adding that the exact location of the hijacking was unclear.

Meanwhile, a spokesman for pirates holding a Saudi supertanker loaded with crude oil has told the BBC a ransom has not been determined. The spokesman said the pirates have spoken to company intermediaries, but found them to be untrustworthy.

Pirates seized the Sirius Star Nov. 15. The supertanker was carrying 2 million barrels of crude oil worth that has been estimated to be worth about $100 million.