Nairobi: Somali pirates seized a Turkish ship with 23 crew on Wednesday and are being shadowed by a Turkish warship in the Gulf of Aden, a shipping official and Nato spokesman said.

The pirates first surrounded the Horizon-1 in speed boats and then boarded the ship, which is carrying sulfate from Saudi Arabia to Jordan, according to Omer Ozgur of Istanbul-based Horizon Shipping.

With the pirates aboard, the ship is continuing on its course with Turkey's TCG Gediz frigate following.

Nato spokesman Cmdr. Chris Davies said the Turkish warship Gediz had seen at least four pirates on the deck of the ship, but others may have been out of sight.

The ship was taken in the Internationally Recommended Transit Corridor, "which is not good news because that's where the ships are meant to be safer," Davies said.

Warships patrol the corridor, where ships are encouraged to travel in groups to help prevent attack.

Attacks in the corridor are rare, and a Turkish warship on escort duty was diverted to the scene shortly after the Horizon-1 sounded the alarm.