U.S. Defense Secretary Jim Mattis awaits the arrival of Vietnamese Defense Minister Gen. Ngo Xuan Lich at the Pentagon in Arlington, Virginia, U.S., August 8, 2017. REUTERS/Kevin Lamarque

WASHINGTON (Reuters) - U.S. Defense Secretary Jim Mattis on Wednesday told North Korea it must stop any action that would “lead to the end of its regime” and “stand down” in its pursuit of nuclear weapons.

These are some of strongest comments Mattis has made on North Korea. In the past he has said that the United States can respond to North Korea, but any military solution would be “tragic on an unbelievable scale.”

“The DPRK must choose to stop isolating itself and stand down its pursuit of nuclear weapons,” Mattis said in a statement. DPRK is short for the North’s official name, the Democratic People’s Republic of Korea.

“The DPRK should cease any consideration of actions that would lead to the end of its regime and the destruction of its people,” Mattis said.

“The DPRK regime’s actions will continue to be grossly overmatched by ours and would lose any arms race or conflict it initiates,” he added.

Mattis added that while the State Department was making diplomatic efforts, the United States and its allies have the most “precise, rehearsed and robust defensive and offensive capabilities on Earth.”

Despite the statement by Mattis, U.S officials say that for now, additional assets have not been moved to the region and the threat assessment has not changed.

The United States has 28,500 troops in South Korea to guard against the North Korean threat. Japan hosts around 54,000 U.S. military personnel, the U.S. Department of Defense says, and tens of thousands of Americans work in both countries.