In response, White House press secretary Sean Spicer reiterated the US security commitment to the allies.

"We stand shoulder to shoulder with Japan and South Korea in doing what we can to protect that region in particular from an attack from North Korea. We understand the situation. We continue to work with them. As I mentioned, the president spoke to both leaders yesterday and we provided a readout of those calls," he said.

"But we obviously understand the concerns of China, but this is a national security issue for them," he said.

On Monday, Trump reaffirmed the US commitment to use the full range of the United States military capabilities to protect South Korea and Japan when he spoke separately with South Korea's acting President Hwang Kyo-ahn and Japanese Prime Minister Shinzo Abe, a day after the North fired a barrage of four ballistic missiles.

Trump also warned that the North will face "very dire consequences" for its provocations.

State Department acting spokesman Mark Toner reiterated THAAD is a purely defensive system.

"I think they've been very clear that THAAD ... is clearly a defensive system. And the reason we're pursuing this implementation or deployment of THAAD is because of North Korea's continued bad behavior," he said. "That they continue to carry out exercises, or rather tests that, frankly, not only threaten the stability of the Korean Peninsula but the region and even the national security of the United States of America."

Toner also said that the issue of THAAD shouldn't be the focus of Secretary of State Rex Tillerson's trip to South Korea, Japan and China next week because the deployment is simply a response to the threat from North Korea.

He also said that the Trump administration is looking at "new initiatives" to address the threat, but declined to discuss specifics. He said that one of the main purposes of Tillerson's trip to the region is to "talk to our allies and partners in the region to try and generate a new approach to North Korea."

"I think right now we're focused on sanctions and implementing those sanctions to the fullest extent possible, but we're looking at other possibilities as well, we always are," Toner said. (Yonhap)