SEOUL, South Korea — North Korea test-launched a suspected long-range missile designed to strike the continental U.S. on Thursday, South Korea’s military said, as a U.S. official warned that North Korean troops in Russian uniforms are heading toward Ukraine.

South Korea’s Joint Chiefs of Staff said it detected a ballistic missile launch from North Korea’s capital region around 7:10 a.m. on Thursday. It said the weapon was launched on a high angle and it was suspected of being a long-range ballistic missile.

The Joint Chiefs of Staff said South Korea’s military has boosted its surveillance posture and was closely exchanging information on the North Korean launch with the U.S. and Japanese authorities.

If confirmed, it’s North Korea’s first test-firing of an intercontinental ballistic missile since December 2023, when it launched the solid-fueled Hwasong-18 ICBM. Missiles with built-in solid propellants are easier to move and hide, and can be launched quicker than liquid-propellant weapons.

South Korea’s military intelligence agency told lawmakers Wednesday that North Korea was close to test-firing a long-range missile capable of reaching the United States and has also likely completed preparations for its seventh nuclear test.

Since 2022, North Korea has sharply increased the pace of its weapons tests to expand its arsenal of nuclear-capable missiles targeting South Korea and the United States. Thursday’s launch was North Korea’s first known ballistic test since Sept. 18, when its leader Kim Jong Un supervised tests of a new type of ballistic missile and a “strategic” cruise missile apparently built to deliver nuclear warheads.

The launch also comes amid concerns that North Korea has dispatched troops to Russia which is fighting a war against Ukraine.

North Korea’s possible participation in the Ukraine war would mark a serious escalation. South Korea, the U.S. and their partners also worry about what North Korea could get from Russia in return for joining Russia’s war against Ukraine. Asides from his soldiers’ wages, experts say North Korean leader Kim Jong Un likely hopes to get high-tech Russian technology that can perfect his nuclear-capable missiles.

On Wednesday, Defense Secretary Lloyd Austin said North Korean troops wearing Russian uniforms and carrying Russian equipment are moving toward Ukraine, in what he called a dangerous and destabilizing development. Austin spoke at a press conference in Washington with South Korean Defense Minister Kim Yong-hyun.

South Korea said Wednesday that North Korea has sent more than 11,000 troops to Russia and that more than 3,000 of them have been moved close to battlefields in Western Russia.