The chief of staff to outgoing US President Barack Obama has said the administration has made it clear to the incoming government of President-elect Donald Trump that North Korea should be a top priority.

In an interview with PBS aired Monday, White House Chief of Staff Denis McDonough said he's concerned about North Korean leader Kim Jong-un's New Year's address about the country's development of an intercontinental ballistic missile.

"We've made that clear since we started these conversations. This goes to the top of the list, that this is a critically important issue, that China needs to understand the importance we attach to it," McDonough said when asked what he wants to say to the incoming government.

"It's a core interest of ours, to not be threatened by North Korea. And that our alliances and our allies need to have confidence that we remain deeply engaged with them as against this threat. And that the North Koreans will continue to feel deeper and deeper isolation," he said.

McDonough said there is "no question" the North Korea issue has moved to the top rank of priorities.

"We've encouraged the next team to take that view as well," he said.

State Department deputy spokesman Mark Toner also said the North should be a key priority for the new government.

"It's one of those issues that when this administration transitions to the new administration is going to remain a serious concern and a serious challenge that we need to address," he said at a regular briefing Tuesday.

Last week, North Korean leader Kim said in his New Year's Day address that the country has reached the final stage of preparation to test-fire an intercontinental ballistic missile, an apparent threat that Pyongyang is close to developing a nuclear-tipped missile capable of striking the continental US.

On Sunday, the North said it will test-fire an ICBM at a time and from a place determined by leader Kim.

US officials have repeatedly stressed the country's fully capable of defending itself and allies, with Secretary of Defense Ash Cater saying the US will "shoot it down" if a North Korean ICBM "were coming towards our territory or the territory of our friends and allies." (Yonhap)