US Defense Secretary Lloyd Austin spoke  with the defense ministers of South Korea and Japan about the threats posed by North Korea after a series of missile launches by Pyongyang, the Pentagon said.

International tension has been rising over a series of North Korean ballistic missile tests, actions long banned by the UN Security Council. January was a record month of such tests, with at least seven launches including a new type of “hypersonic missile” able to maneuver at high speed.

“The leaders emphasized that the DPRK’s ballistic missile launches are destabilising to regional security and a clear violation of multiple United Nations Security Council resolutions,” Pentagon spokesman John Kirby said in a statement, using the acronym for North Korea’s official name.

North Korea boasted on Tuesday that it is one of only a handful of countries in the world to field nuclear weapons and advanced missiles and the only one standing up to the United States by “shaking the world” with missile tests.

An excerpt of a confidential United Nations report said that North Korea continued to develop its nuclear and ballistic missile programs during the past year and cyberattacks on cryptocurrency exchanges were an important revenue source for Pyongyang.