A White House official on Thursday expressed concern over a new security treaty between Russia and North Korea, and vowed to continue to evaluate America's defense posture throughout the Indo-Pacific "as needed."

National Security Communications Advisor John Kirby made the remarks after Russian President Vladimir Putin and North Korean leader Kim Jong-un signed a comprehensive strategic partnership treaty during a summit in Pyongyang on Wednesday.

The treaty stipulates that in case any one of the two sides is put in a state of war by an armed invasion, the other side will provide military and other assistance with "all means" "without delay" in accordance with the UN Charter and relevant Russian and North Korean laws.

"Of course, it is (a concern). It's to be of concern to any country that cares about maintaining peace and stability not just on the Korean Peninsula, but in the Indo-Pacific," he said during an online press briefing.

"It should be a concern to any country that believes that the UN Security Council resolutions ought to be abided by. It should be a concern to anybody who thinks that supporting the people of Ukraine is an important thing to do," he added.

Stressing President Joe Biden's policy focus on strengthening alliances for regional peace, Kirby pledged US efforts to continue to ensure stability in the Indo-Pacific.

"Of course, we are going to continue to evaluate our posture throughout the Indo-Pacific as needed, but we have prioritized this part of the world since the beginning of this administration," he said.

"That effort, we believe, has right now and will continue to put us in the best possible position ... for any threats and challenges not just on the Korean Peninsula but elsewhere in the region," he added.

Kirby also stressed that Beijing would also share the concern about the recent development in cooperation between Moscow and Pyongyang.

"We would think that that concern would be shared by the People's Republic of China since this agreement also seems to be in direct contrast with the statement that President Putin and President Xi (Jinping) made in Beijing just a month ago, in which both countries call for a peaceful and diplomatic solution to this situation on the Korean Peninsula," he said.

PRC stands for China's official name.

In a separate press briefing, Pentagon press secretary Maj. Gen. Pat Ryder commented on the new treaty between Moscow and Pyongyang, saying the US will monitor related developments "very closely."

"There is no surprise here that they have been developing and fostering this relationship. ... It is something that we are going to continue to monitor," he said.

"But what we've also said is that our focus, when it comes to the Indo-Pacific region, and broadly speaking worldwide, is to work with like-minded nations on security and stability throughout the world to include the Indo-Pacific region," he added.

Ryder stressed the "defensive" nature of the South Korea-US alliance, reaffirming America's "ironclad" security commitment to its Asian ally.

He also said that the summit between Putin and Kim showed how Russia is "isolated."

"I just think it demonstrates the desperation that a country like Russia needs to align itself with the DPRK to subjugate the people of Ukraine and the fact that they have to go to a country like the DPRK to obtain munitions," he said.

DPRK stands for the North's official name, the Democratic People's Republic of Korea. (Yonhap)