Washington (CNN) National security adviser John Bolton said Tuesday that President Donald Trump believes he should hold a second summit with Kim Jong Un because the North Korean leader hasn't lived up to commitments he made during their first meeting.

"They have not lived up to the commitments so far," Bolton said at The Wall Street Journal's annual CEO Council conference in Washington. "That's why I think the President thinks that another summit is likely to be productive."

Bolton said the US would press ahead with a second meeting shortly after the start of the new year -- saying, "January, February" -- in the hope of making further progress. He said the Trump administration would not lift hefty economic sanctions against the regime until then.

'Getting along'

The national security adviser's comments underscored the lack of progress the US has made in moving North Korea closer to the complete, verifiable and irreversible denuclearization Washington is seeking, and the concessions it has been making to Pyongyang, even as Trump has stressed the warmth of his relationship with Kim.

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