U.S. Deputy Secretary of State Kurt Campbell said Wednesday that Washington and its allies are “alarmed” by North Korea’s nuclear and missile threats as well as its increasing military support for Russia’s war in Ukraine, but said he couldn’t confirm Ukrainian claims that Pyongyang was also sending soldiers to fight for Moscow.

Campbell spoke with reporters following discussions with South Korean and Japanese counterparts on reinvigorating an international pressure campaign against North Korea, which faltered in recent years amid a deepening divide at the U.N. Security Council.