In his first public remarks since being fired by tweet three weeks ago, Bolton said dictator Kim Jong Un -- whom Trump has cultivated as a friend in an attempt at convincing him to surrender his nuclear program -- will "do whatever he can" to keep a nuclear weapons capability.

"Under current circumstances he will never give up the nuclear weapons voluntarily," Bolton said in remarks at the Center for Strategic and International Studies, a think tank in Washington.

It was a stark break from Trump's stated goal in his talks with Kim, which he says are proceeding well, despite little indication from the North it is willing to abandon its nuclear weapons.

Trump has cited a lack of nuclear and long-range missile tests as evidence his strategy is working. But Bolton dismissed that view, saying the reason the North has stopped those tests is the technology is already in place.

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