A top U.S. Defense Department official has been quoted as saying that the U.S. does not wish to see South Korea and Japan go nuclear in response to North Korea's nuclear and missile threats.

According to Japan's Jiji Press, the unnamed official told Japanese reporters that Washington will bolster its nuclear umbrella for stronger deterrence and will fulfill its duty to protect its South Korean and Japanese allies against North Korean threats.

The official said Pyongyang's short-range missiles are a bigger threat to Seoul and Tokyo than long-range missiles. He said North Korea's short-range missile launches last week violated U.N. Security Council resolutions.