South Carolina Senator Lindsey Graham speaks about North Korea

"He has genuine concern about the direction of events in North Korea".

Trump's "fire and fury" remark on Tuesday followed reports that North Korea produced a nuclear weapon small enough to fit inside a missile.

Clapper appeared to reference Trump's tweet in January, following reports of an unverified dossier that purportedly had damaging information on Trump.

"I think that's the right call because we can't live as a nation under the threat of nuclear attack from a insane man in North Korea،" Graham added.

"I was really struck when I visited there in November 2014, you know, but the level of paranoia and the siege mentality that prevails in North Korea was overwhelming", Clapper explained. The last serious U.S.

North Korea's weapons program has developed significantly since then.

Any negotiation would face huge skepticism in Washington given North Korea's long record of broken promises.

President Trump suggested that his earlier warning to North Korea that it would be "met with fire and fury" if it continued to threaten the U.S.

On Thursday, the President said his message may not have been "tough enough".

"The UK stands shoulder to shoulder with the tackling this threat and many others".

However, statements from North Korea suggest that no move will be made until the U.S. attacks North Korea first. Warmbier, 22, was held in North Korea for 17 months and returned to the a coma.

"I think he really had in mind John Brennan and myself, and perhaps as things unfolded, Jim Comey", Clapper said, referring to former Central Intelligence Agency director John Brennan and former Federal Bureau of Investigation director James Comey.

If North Korea launches ballistic missiles aimed at waters around Guam, the United States will counter the threat by intercepting them with Aegis destroyers deployed in the East China Sea and the Pacific Ocean, as well as the Terminal High Altitude Area Defense (THAAD) missile defense system deployed on the island.

Neither the White House nor the State Department commented on Yun's communication channel, and a diplomat at North Korea's United Nations mission confirmed to the AP only that the channel had been used to negotiate Warmbier's release.