A Turkish cargo vessel seized three days ago has been abandoned by Somali pirates, leaving all 25 crew unharmed, Turkish officials say.The Yasin C came under attack on Wednesday off the Kenyan coast as it headed toward its destination, Mombasa. The crew locked themselves in the engine room and did not emerge until they knew they were safe. The US navy has meanwhile clashed with suspected pirates in the Gulf of Aden after they fired on a navy vessel. Six suspected pirates were captured after the clash. A spokesman for Bergen Shipping, which operates Yasin C, said the 22,353-tonne vessel had been safely retrieved. "The ship's captain gave the good news that the pirates had abandoned the ship," Fatih Kabal told Turkey's state-run news agency Anatolian.It was not clear why the Yasin C was abandoned. However observers say pirates have been known to abandon a vessel if they believe it has no ransom value, or if it develops mechanical problems or is short on fuel. In recent years, pirates have seized dozens of ships in the Indian Ocean and Gulf of Aden and recently expanded the reach of their attacks.