LONDON (AP) — U.S. Defense Secretary Jim Mattis is expressing worry about what he calls "reckless" actions by North Korea, alluding to its nuclear weapons and missile programs.

Mattis spoke at a news conference Friday in London with his British counterpart, Michael Fallon.

Mattis raised the North Korea issue in response to a reporter's question about Iran. Mattis suggests that North Korea is a more urgent problem.

North Korea is reportedly preparing a new nuclear test. Mattis says North Korea has "got to be stopped."

A reporter noted that Mattis, as head of U.S. Central Command in 2012, had said Iran was the main threat facing the United States. In responding, Mattis quickly pivoted to North Korea, which has rattled Washington with threats to attack the U.S. with nuclear missiles.

"In the larger scheme of things," Mattis said, North Korea is the more urgent threat.

"This is a threat of both rhetoric and growing capability," Mattis said, adding that the North Koreans are acting "in a very reckless manner" and "have got to be stopped."