Washington's top diplomat says although he is aware negotiating denuclearization with North Korean leader Kim Jong-un is a tough challenge, "it's the mission set."

In an interview with Fox Business Network on Wednesday, U.S. Secretary of State Mike Pompeo also revealed former President Barack Obama told his successor during their transition period that the North Korean issue will pose the biggest threat.

He added that former U.S. governments had left the North Korean regime to continue posing such threat for decades.

Pompeo said the Donald Trump administration's direct approach of applying pressure on Pyongyang with international sanctions is the reason why President Trump is able to have one-on-one talks with his North Korean counterpart.

Pompeo said when the two leaders meet for the second time in Vietnam later this month, the U.S. is ready to support the North so it can fulfill its denuclearization commitments and offer a better future for its people.