However, North Korea responded with threats that any attempt to search one of its ships would be considered "an act of war" and would be "met with a decisive military response".
Meanwhile, Kim Jong-il has paid a morale-boosting visit to the troops, according to the North Korean state news agency.
Kim told soldiers of the 7th Infantry Division that he was greatly satisfied that the army "had been prepared to perform its combat duty in any circumstance".
According to the North Korean state media, Kim "highly praised" the soldiers for their "militant training spirit" and told them that "Training is also a battle!".
North Korea claims US could provoke nuclear war - Telegraph