His warning follows a North Korean state-controlled newspaper on Sunday accusing the U.S. of "double-dealing" and "hatching a criminal plot" against Pyongyang after Washington abruptly canceled a visit by Secretary of State Mike Pompeo.
The decision to cancel Pompeo's trip appeared to have been made abruptly, coming just a day after Pompeo announced it would happen.
Since Trump's summit with North Korea dictator Kim Jong Un, the U.S. has called off its military exercises with South Korea while China and Russia have softened pressure on North Korea.
"We are worse off than where we were when the summit happened because, in the meantime, China and Russia have alleviated sanctions pressure on North Korea. We've also unilaterally canceled our military exercises with South Korea with our own president even labeling these exercises provocative which certainly unnerved Japan," said Sean King, senior vice president at public policy and business development firm Park Strategies.