North Korea probably cannot launch nuclear-armed missiles, Seoul sources said today, downplaying fears of a strike by the reclusive regime, ahead of a visit by the US Secretary of State.

“North Korea has conducted three nuclear tests, but it is still doubtful that North Korea has made a small, light warhead that can be mounted on a missile,” Defence Ministry spokesman Kim Min Seok said in a press briefing.

On Thursday, US Congressman Doug Lamborn said North Korea has nuclear warheads that could be delivered by ballistic missiles, citing a report by the Defence Intelligence Agency.

But the Pentagon denied the assessment. “It would be inaccurate to suggest that the North Korean regime has fully tested, developed, or demonstrated the kinds of nuclear capabilities referenced in the passage,” spokesman George Little said on Thursday.

Recent threats by North Korea and concerns over its nuclear capability were expected to top the agenda in the first visit by John Kerry as US Secretary of State to South Korea later today.