CNN  — 

Ousted national security adviser John Bolton made clear Monday his sharp disagreements with his former boss, President Donald Trump, on North Korea, saying he didn’t believe Pyongyang would willingly surrender its nuclear weapons.

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.

In June, Trump said North Korean leader Kim Jong Un has “kept his word” when it comes to nuclear and missile testing – a direct contradiction of Bolton, who just hours earlier had accused Pyongyang of failing to follow through on its commitments.

Bolton, who left the administration isolated among Trump’s other advisers, acknowledged at the start of his remarks he was speaking as a private individual.

“I am delighted to be here today. I’m also sure the leadership of North Korea is delighted I am here today in a private capacity, at least that’s what I’ve read,” he said. “Perhaps they’ll be a little less delighted now that I can speak in unvarnished terms about the grave and growing threat that the north Korean nuclear weapons program poses to international peace and security.”

He took few steps to disguise his disagreements with Trump. He even again raised the so-called “Libya model” for denuclearization, a reference that enraged Trump when Bolton first mentioned it last year since it seemed to temporarily derail his diplomatic efforts with Kim.

Describing the current situation with North Korea as a “classic standoff,” Bolton said the country’s leaders “want a piece of something that we should not be prepared to give them.”

Earlier this month, Bolton offered scathing criticism of Trump’s approach to Iran, North Korea and Afghanistan at a private event hosted by the Gatestone Institute in New York.

“Bolton didn’t have anything positive to say about Trump,” one attendee said.

While Bolton did not mention Trump by name, he said the idea of inviting the Taliban to Camp David was “disrespectful” to the victims of the September 11, 2001, terrorist attacks, according to the attendee. As CNN previously reported, Bolton and Trump got into a heated argument over the President’s plan to host the Taliban leaders in the days before the 18th anniversary of the attacks, and Bolton did not back down, two people familiar with what happened said.

One senior official confirmed this argument happened in the Oval Office and at the end of the meeting, the President asked Bolton for his resignation.

CNN’s Jim Acosta and Paul LeBlanc contributed to this report.