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.

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Earlier on Wednesday, Washington, Seoul and Tokyo announced plans with eight Western governments to launch a new multinational team to monitor the enforcement of sanctions against North Korea.

Russia in March vetoed a U.N. resolution in a move that effectively abolished monitoring by U.N. experts of Security Council sanctions against North Korea, which prompted Western accusations that Moscow was acting to shield its arms purchases from Pyongyang to fuel its war in Ukraine.

Campbell said there are signs that North Korea was increasing its support of materials, including artillery and missiles, to support Russia’s war on Ukraine, which he said was “creating further instability in Europe.” He said the U.S. was still evaluating reports that North Korea was also sending personnel.

“We are concerned by them and ... we agreed that we will continue to monitor the situation closely,” Campbell said about the claims.

Ukrainian President Volodymyr Zelenskyy has claimed that North Korea is sending military personnel to help Russia’s war effort without providing details. Ukrainian media reported earlier this month that six North Koreans were among those killed after a Ukrainian missile strike on Oct. 3.

North Korea has also been making increasingly provocative threats against rival South Korea, including accusing the South of infiltrating drones to drop anti-North Korean propaganda leaflets over Pyongyang and threatening to attack the South if it happens again. North Korea also on Tuesday blew up the northern sections of unused road and rail routes that once linked it with South Korea, in a choreographed demolition aimed at demonstrating its growing anger with South Korea’s conservative government.

Tensions on the Korean Peninsula have spiked since 2022 as North Korean leader Kim Jong Un used Russia’s war on Ukraine as a window to dial up his weapons testing activities and threats. Washington, Seoul and Tokyo have strengthened their combined military exercises in response and took steps to sharpen their nuclear deterrence strategies built around strategic U.S. assets.

Following his talks with Campbell and Japanese Vice Foreign Minister Masataka Okano, South Korean Vice Foreign Minister Kim Hong Kyun said that the countries condemn the North’s “intentional moves to create tensions.”

“We have agreed to maintain a solid South Korea-U.S. combined posture to respond firmly to North Korean provocations and strengthen security cooperation through close coordination between South Korea, the U.S., and Japan,” Kim said.