President Trump's national security adviser, H.R. McMaster, said on Sunday the U.S. needs to move "with a great deal of urgency" in response to the North Korean threat.

McMaster told "Fox News Sunday" that North Korea is close to threatening the U.S. with a nuclear weapon.

"We really have to move with a great deal of urgency, on sanctions, on diplomacy and on preparing, if necessary, a military option," McMaster said.

ADVERTISEMENT

McMaster was also asked about Trump's tweet earlier Sunday, when the president appeared to refer to North Korea's leader as "Rocket Man."

"I spoke with President Moon [Jae-in] of South Korea last night. Asked him how Rocket Man is doing. Long gas lines forming in North Korea. Too bad!" Trump tweeted.

McMaster said that's "a new one" for the president.

"Of course that's where the rockets are coming from," McMaster said, before adding that people shouldn't laugh about them because they represent a great threat.