NAIROBI , Kenya ( CNN ) -- A Yemeni freighter has become the latest commercial vessel to be attacked in the pirate-plagued Gulf of Aden , a Kenyan maritime official said Tuesday . A French frigate shadows a commercial ship leaving Djibouti harbor on its way to the Gulf of Aden . The last contact with the ship was late last week , and it was unclear exactly when the hijacking took place , said Andrew Mwangura , the head of Kenya Seafarers Association . No further details about the ship , its crew or cargo were immediately available , said Mwangura , whose organization keeps tabs on the welfare of sailors captured by the pirates . Dozens of ships have been attacked in the Gulf of Aden by pirates based in largely lawless Somalia in recent months . This has led to calls from commercial ship owners for a military blockade along the coast of Somalia to intercept pirate vessels heading out to sea . Peter Swift , managing director of the International Association of Independent Tanker Owners , said stronger naval action -- including aerial and aviation support -- is necessary to battle rampant piracy in the region . Watch more about the growing piracy problem » . At present , warships from a number of countries patrol an international maritime corridor , escorting some merchant ships and responding to distress calls in the area . But the navies involved say it is virtually impossible to patrol the vast sea around the gulf . Meanwhile , a spokesman for pirates holding a Saudi supertanker loaded with crude oil has told the BBC they have not set any ransom figure . He said the group has only spoken to intermediaries of the vessel 's owners but he described them as untrustworthy . The pirate identified himself using only one name , Daybad , when he spoke late Monday to the BBC . Pirates seized the Sirius Star on November 15 in their most audacious hijacking to date . The vessel is carrying two million barrels of crude oil worth about $ 100 million . Elsewhere , the head of U.S. military operations in Africa has said he does not have any evidence that Somali pirates are connected to al Qaeda . The Africom chief , Army Gen. William `` Kip '' Ward , told The Associated Press Tuesday that the chaos off Somalia 's high seas is a reflection of the country 's political chaos . Asked about alleged connections between pirates and al Qaeda , he said : `` I think that 's a concern that we all would have . '' But he added that he does n't have `` any evidence that pirates have links to al Qaeda . ''
Last contact with the Yemeni freighter was late last week . Dozens of ships have been attacked by pirates in the Gulf of Aden . Report : No ransom figure yet for hijacked Saudi supertanker . Score: 7