SEOUL, South Korea — 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 and increasing military support for Russia’s war in Ukraine, but said he rejects Ukrainian claims that Pyongyang also sends soldiers to fight for Moscow.

Campbell spoke to reporters after talks with South Korean and Japanese counterparts about reviving an international pressure campaign against North Korea, which has faltered in recent years amid a widening rift within the U.N. Security Council.

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

Russia vetoed a U.N. resolution in March that effectively abolished U.N. experts’ oversight of Security Council sanctions on North Korea. This led to Western accusations that Moscow was acting to shield its arms purchases from Pyongyang in order to fuel the war in Ukraine.

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

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

Ukrainian President Volodymyr Zelensky 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 the dead after a Ukrainian missile attack on October 3.

North Korea has also made 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 this happens again. North Korea also blew up the northern portions of unused road and rail lines that once linked it to South Korea on Tuesday, in a choreographed demolition intended to demonstrate its growing anger toward South Korea’s conservative government.

Tensions have risen on the Korean Peninsula since 2022 when North Korean leader Kim Jong Un used Russia’s war against Ukraine as an opportunity to increase his weapons testing activities and threats. In response, Washington, Seoul and Tokyo have stepped up their combined military exercises and taken steps to sharpen their nuclear deterrent strategies, which are built around strategic US assets.

After his talks with Campbell and Japanese Vice Foreign Minister Masataka Okano, South Korean Vice Foreign Minister Kim Hong Kyun said the countries condemned the North’s “deliberate attempts to create tensions.”

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