The United States is considering deploying an advanced missile-defense system in South Korea.Quoting Pentagon officials, the Wall Street Journal says Washington has conducted a site survey for possible deployment locations for its Theater High Altitude Area Defense, or THAAD.No final decision has been made yet on the system which is designed to intercept a diverse range of missiles.The Vice Chairman of the U.S. Joint Chiefs of Staff James Winnefeld is calling on South Korea and Japan to cooperate on the issue.Speaking at a think-tank in Washington Wednesday, Winnefeld emphasized the importance of developing a regional missile defense system in the face of continued North Korean threats.