Defense Secretary Jim Mattis declared North Korea the "most urgent and dangerous threat to peace and security," before the House Armed Services Committee on Monday night, moving Kim Jon Un's regime past Russia as the No. 1 threat the United States faces.

The statement was included in the defense secretary's prepared opening statement, five months after Mattis identified Russia as first among threats facing the United States. The change comes as Pyongyang moves forward with what the United States calls an unprecedented number of tests on nuclear weapons and ballistic missiles, and as the Trump administration's connections to Russia are scrutinized by the FBI.

"North Korea's continued pursuit of nuclear weapons and the means to deliver them has increased in pace and scope," Mattis said. "The regime's nuclear weapons program is a clear and present danger to all, and the regime's provocative actions, manifestly illegal under international law, have not abated despite United Nations' censure and sanctions."

But Mattis still identified Russia as a threat, along with China, Iran and terrorist organizations. Russia and China, he said, are both "resurgent and more aggressive," and have placed the "international order under assault." The secretary has sought to reassure allies in both Europe and the Pacific in recent months that the United States still stands with them, after President Donald Trump repeatedly raised questions about whether he was committed to longstanding military alliances.

Mattis appeared alongside Marine Gen. Joseph Dunford, the chairman of the Joint Chiefs of Staff, and Pentagon comptroller David Norquist. In Dunford's prepared testimony, he did not list a No. 1 threat, but labeled Russia, China, Iran, North Korea and terrorist groups as "key challenges" the United States faces.

Several senior defense officials aside from Mattis have declared Russia the top threat the United States faces in the last few years, including Dunford. But the United States and Russia have forged an uneasy, limited relationship in some areas over the past year, including deconflicting aviation operations over Syria as the Pentagon goes after Islamic State militants and Russia backs the Syrian regime.

Senior U.S. officials have sought recently to get China, a strong trade partner of North Korea, to put diplomatic and economic pressure on Pyongyang to get them to back down from moving ahead with their weapons programs. But it's uncertain if they will, and Trump has threatened that the United States will take care of the North Korean threat on its own if China won't help.

Last week, Navy Vice Adm. James Syring, the director of the Missile Defense Agency, declined to say before the House subcommittee on strategic forces that the United States is "comfortably ahead" of the threat North Korea poses with an intercontinental ballistic missile.

"It is incumbent upon us to assume that North Korea today can range the United States with an ICBM carrying a nuclear warhead," he said. "Everything that we are doing plans for that contingency . . . in addition to looking ahead to what might be developed or what is possible over the next five to ten years."

Mattis, asked Monday if the threat posed by ballistic missiles is growing, said that the threat is growing, but that existing missile-defense systems stationed at Fort Greely in Alaska and Vandenberg Air Force Base in California pose an adequate amount of protection as the Pentagon examines long-term options. Among them is adding a missile-defense site somewhere on the East Coast, he added.

"Every time they fire one of these, they're learning something more so it's a worsening situation," Mattis said. "But we can buy the time right now."

Dunford, asked about the threat, said that the United States balances its missile-defense systems with other ways to counter North Korea, including cyber warfare, Navy weapons and intelligence collection.