He said the North is the most immediate threat to the security of the US, South Korea and Japan.

"Make no mistake; Kim Jong Un is making progress on his quest for nuclear weapons and a means to deliver them intercontinentally.

All nations need to take this threat seriously because North Korea's missiles point in all directions," the commander said.

"North Korea's capabilities are not yet an existential threat to America, but if left unchecked, it will eventually match the capability to hostile rhetoric," he said.

The commander also said the crisis on the Korean Peninsula is "real as the worst I've seen."

Harris said that the US has seen "more activity, proactive, positive activity" from China in trying to rein in the North, but he won't "bet my farm on it."

Chairman John McCain said that the North is making real progress in developing nuclear missiles.

"A North Korean missile with a nuclear payload capable of striking an American city is no longer a distant hypothetical, but an imminent danger, one that poses a real and rising risk of conflict," the senator said.

McCain also said it is "shameful" that China has been bullying South Korea for hosting the US THAAD missile defense system aimed at defending better against North Korean missile threats.

"This committee understands that deploying this system is a joint alliance decision that is necessary to defend our ally, South Korea," he said. (Yonhap)