Washington  - The captain of the US-operated cargo ship that was hijacked off the coast of Somalia on Wednesday has been taken hostage, a crew member confirmed.

Captain Joseph Murphy was being held by the pirates on the ship's lifeboat and was alive, second mate Ken Quinn told broadcaster CNN.

He also said that the crew was in control of the ship and was waiting for additional support from a US Naval destroyer, which was about three hours away.

"We took one of the pirates hostage. We tied him up and kept him for 12 hours. We returned him, but they didn't return our captain," Quinn said.

"They're (pirates) not aboard. We're in control of the vessel. We can hear our captain - he's got a ship radio."

The ship with 20 US citizens on board was taken by Somali pirates early Wednesday morning, the first time a US crew has been taken hostage in the volatile waters.

Owned by Danish firm Maersk and operated by US company Maersk Line Limited, the ship was carrying food supplies and no weapons, and was headed to Mombasa, Kenya, according to John Reinhart, chief executive of Maersk Line. (dpa)