Donald Trump is "losing the plot" on North Korea and is generating a lot of anxiety within the region, according to an academic who specialises in the country.
John Nilsson-Wright also told Julia Hartley-Brewer that Kim Jong-un is a "shrewd poker player" who thinks he has "an invincible hand."
The United Nations Security Council is to convene after the regime in Pyongyang conducted a nuclear test, triggering an artificial earthquake felt in Russia and China.
Photos surfaced of Kim Jong-un examining a nuclear warhead as it was being fitted to the nose of an intercontinental ballistic missile.
The news has brought international condemnation, and the Trump administration warned it would respond in force if the US or its allies were threatened.
Dr John Nilson-Wright, a senior research fellow for Northeast Asia at Chatham House, told Julia Hartley-Brewer: "The President is being so cavalier in his public statements. It’s a worry in Seoul, it’s a worry in Tokyo.
"We saw the US President criticising the South Koreans’ so-called appeasement and at the same time and threatening to tear up the US-Korea free trade agreement - an astonishing and irresponsible act at a time when the Koreans are facing probably their gravest crisis in their history as a state when it comes to relations with North Korea.
“This is the worst time - if there is ever a good time to engage in those economic forms of brinkmanship.
"President Trump is losing the plot, again, I’m afraid, and generating a lot of anxiety in the region."
Kim, on the other hand, "a very shrewd who thinks he's got an invincible hand. And in some ways... it's easy to see why he believes that.
"He doesn't need to go much further in terms of deploying a warhead on a long-range missile. The fact that he seems so clearly a present, a real danger to his neighbours means he can thumb his nose at Donald Trump with impunity."
The question now is "at what point does Donald Trump's patience snap."