The President's comments come amid heightening tensions over North Korea's nuclear weapons program, with Trump tweeting earlier this week that his nuclear button is "bigger and more powerful" the Kim's.
"So I'm behind that 100 percent", the president told reporters at Camp David.
"He knows I'm not messing around, not even a little bit", Trump said.
"I think like most of us they're trying to figure it out, but giving the long history between the (U.S. and North Korea), they'll lean towards the most negative interpretation possible", said Andray Abrahamian, a visiting fellow at the CSIS Pacific Forum. "At the appropriate time, we'll get involved".
Trump can be serious about direct talks with the North Korean leader because he wants to compensate his low-approval rating prior to the mid-term election with diplomatic breakthrough, said Kim Yeol-Su, senior researcher at the Korea Institute for Military Affairs.
Seoul and organizers are keen for the North to take part in the Games to help ease tensions.
The Japanese news agency said Chang made the brief comment to reporters during a stopover at Beijing's worldwide airport.
Pyongyang past year carried out its sixth and most powerful nuclear test and test-launched three intercontinental ballistic missiles, as it attempts to develop nuclear missiles that are capable of striking the United States mainland. It appeared to be a softening of rhetoric, given that Trump lectured Secretary of State Rex Tillerson a year ago that it would be a waste of time "trying to negotiate with Little Rocket Man", Trump's nickname for Kim.
Addressing a CPI (M) district committee meet at Kozhikode on Wednesday, he said North Korea was showcasing a better example in defending "imperialist" forces. "They've been giving everything".
The following day, South Korea proposed to talk in Panmunjom on that and other issues as the resumption of meetings of families separated by the war of the 1950 decade and the development of the industrial complex of Kaesong.
News agency RIA Novosti quoted him as saying that Moscow "observes with satisfaction" that their calls to halt the manouevres have been "taken into account".
The North sees these drills as preparations for invasion and just cause for its weapons programmes, that it conducts in defiance of UN Security Council resolutions.
The latest round of sanctions passed in December bans the supply of almost 75 percent of refined oil products to North Korea, puts a cap on crude deliveries and orders all North Korean nationals working overseas to be sent back by the end of 2019.