Secretary of State Pompeo is prepared to go back to North Korea to meet with Kim Jong Un. We’ve proposed that in our most recent letter from the president to Kim Jong Un,” Bolton said in an interview on Fox News Channel on Tuesday .

UN experts said North Korea had not suspended its nuclear and ballistic missile programs, saying it was a violation and a challenge to UN sanctions against Pyongyang.

North Korea said on Saturday that the United States was acting with impatient patience over denuclearize, while US Secretary of State Mike Pompeo stressed the need to "keep the pressure" on Pyongyang by enforcing sanctions.