He did not provide further details. Biegun travelled to Pyongyang earlier this month for three days of preparatory meetings with North Korean officials, with the State Department saying the talks focused on Trump and Kim's "commitments of complete denuclearisation, transforming US-DPRK relations and building a lasting peace on the Korean Peninsula".
But progress has since stalled with the two sides disagreeing over what that means and analysts say tangible progress on denuclearisation will be needed for the second summit if it is to avoid being dismissed as "reality TV".
Trump's own intelligence chief, Dan Coats, have expressed scepticism over the North's denuclearisation, and told the Senate Intelligence Committee that Pyongyang was "unlikely to completely give up its nuclear weapons".
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