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.