Somali pirates demanded a 19 million pound ransom on Saturday for a Ukrainian ship they seized carrying 33 tanks and other military supplies to Kenya, a maritime official said, according to Reuters.
"The gunmen are demanding $35 million (19 million pounds) to release the MV Faina and her crew," said Andrew Mwangura of the Mombasa-based East African Seafarers' Assistance Programme.
Kenya's military said they had not made contact with the Somali pirates holding the ship, local media reported.
The 21 crew members aboard the ship include 17 Ukrainians, Russians and Latvians.
Mwangura said a Greek ship, Genious, flying a Liberian flag, was hijacked in the same area on Friday with 19 Romanian crew on board. He had no further details.
He said pirates had released a Malaysian chemical tanker, Bunga Melati 5, on Saturday after a $2 million ransom was paid.
"The ransom was delivered by Malaysian navy who were in the area," he said. A Japanese ship was released late on Friday.
Pirates have captured more than 30 vessels off Somalia this year, making its waters the most dangerous in the world and threatening a globally important shipping lane between Europe and Asia. The gangs seek, and often receive, large ransoms.
The Ukrainian ship, sailing under a Belize flag, is carrying 33 T-72 tanks as well as grenade launchers and ammunition bound for Kenya.
The haul is a significant seizure in Somalia, where Islamist insurgents have been fighting the government and its Ethiopian military ally for nearly two years.
Kenyan media reported that the pirates had warned against any rescue attempts. Kenya's government said it would not negotiate with pirates.
"We will endeavour to recover the hijacked ship and military cargo," a government statement said.
Russia's navy said it had sent a warship to Somalia's Indian Ocean coast to conduct anti-piracy patrols in the area.