U.S. Secretary of State John Kerry arrived in Seoul on Friday (April 12) just hours after a U.S. government agency said North Korea had a nuclear weapon it could mount on a missile, but the assessment was swiftly dismissed by several U.S. officials and South Korea.

North Korea will dominate talks when Kerry meets South Korea's leadership in Seoul, including South Korean President Park Geun-hye and Foreign Minister Yun Byung-se later on Friday.

The Defense Intelligence Agency (DIA) said it had concluded with "moderate confidence" that North Korea had developed a nuclear bomb that could be fitted on a ballistic missile, but added such a weapon would probably be unreliable.

Its assessment was made public by a U.S. lawmaker amid soaring tension on the Korean peninsula and just hours before Kerry arrived on a visit to the region that will include stops in China and Japan.

North Korea has stationed as many as five medium-range missiles on its east coast, according to