"The fact is we inherited a mess. It's a mess," Trump said, picking the Middle East and North Korea as examples of such problems. "North Korea, I'll tell you what, what's happening there is disgraceful and not smart, not smart at all. So many different problems."

It was the latest in a series of remarks Trump has made about the North in recent days.

On Friday, Trump tweeted, "North Korea is behaving very badly.

They have been 'playing' the United States for years. China has done little to help!" He also said on Sunday that North Korean leader Kim Jong-un is acting "very, very badly."

That appears to show the problem weighs on Trump's mind.

Former President Barack Obama reportedly warned Trump that North Korea will be one of Trump's biggest foreign policy problems when they met at the White House after Trump's election.

The White House has been putting together a new strategy to deal with the North, and the focus is expected to be on ramping up pressure on Pyongyang, rather than reopening negotiations.

Secretary of State Rex Tillerson said during a trip to South Korea and Japan last week that two decades of diplomatic efforts to disarm the North failed, and there was no point in pursuing the diplomatic path any longer. He also said that the US was considering a wide range of options, including the use of military force.

In response, the North said it is fully ready for "any war." (Yonhap)