The chairman of the U.S. Joint Chiefs of Staff, Admiral Mike Mullen, says that the North Korean leadership is unpredictable and that it is important to continue to pursue a policy of isolation against North Korean leaders.

He made the remarks in a meeting with U.S. forces stationed in Afghanistan on Sunday.

Mullen stressed the need to increase pressure on North Korea, saying that the future actions of the leaders of the communist state are unpredictable.

He said North Korea’s sinking of the “Cheonan” has strengthened the U.S.-South Korean alliance.