SEOUL—South Korea has asked the U.S. to consider delaying the planned 2015 transfer of wartime control of South Korean forces to Seoul's command because of North Korea's nuclear threat, the country's defense ministry said Wednesday.

Under existing plans, South Korea is slated to gain by December 2015 full command of its own armed forces in the event of war. The U.S. has assumed this responsibility since the end of hostilities in the Korean War in 1953.

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