Police say they had found nothing unusual on a Greek-owned ship docked at the southwestern port of Kunsan.

Investigators searched the ship for weapons or forged passports after a tip-off from a U.S. intelligence source it could be carrying members of Osama bin Laden's al Qaeda terrorist group.

But a port official said that authorities will keep watching the ship until it leaves the country.

The Athena, flying the Bahamas flag, arrived in Kunsan with its cargo of timber on Thursday and is scheduled to stay for up to 10 days.

Greek shipping company Petrobulk Maritime, which owns the vessel, said on Thursday South Korean investigators had found nothing suspicious and left the ship after apologizing.

On Wednesday, the Munhwa Ilbo newspaper quoted unidentified military sources as saying the U.S. military had tipped-off South Korean officials about the ship.