In a statement North Korea agreed to work towards "complete denuclearisation of the Korean Peninsula".
But the document has been criticised for lacking details on when or how Pyongyang would give up its weapons.
But he added: "Major disarmament... We're hopeful that we can achieve that in the two and half years."
He said he was confident Pyongyang understood the need for verification that it was dismantling its nuclear programme.
The credibility of that claim is in doubt. That is because under the deal, the North retains its nuclear warheads, the missiles to launch them and has not agreed to any specific process to get rid of them.
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