South Korean Marines patrol in the snow on Yeonpyeong Island, South Korea, Wednesday, Dec. 8, 2010. The top U.S. military officer on Wednesday warned North Korea that the U.S. commitment to helping South Korea defend itself is "unquestioned," even as he pressed China to use its influence to rein in its ally Pyongyang. (AP Photo/Yonhap, Kim hyun-tae)

Photo by: Kim Hyun-tae

South Korean Marines patrol in the snow on Yeonpyeong Island, South Korea, Wednesday, Dec. 8, 2010. The top U.S. military officer on Wednesday warned North Korea that the U.S. commitment to helping South Korea defend itself is "unquestioned," even as he pressed China to use its influence to rein in its ally Pyongyang. (AP Photo/Yonhap, Kim hyun-tae)