WASHINGTON — Growing evidence of an expanding military partnership between North Korea and Russia is sparking renewed concern in Washington, where officials see Moscow making a determined but desperate push to advance in its war against Ukraine. The heightened sense of unease follows allegations Friday by U.S. ally South Korea that North Korea sent 1,500 troops from its special forces to Vladivostok, Russia, earlier this month, with plans for additional deployments in the works. South Korea’s National Intelligence Service said that it identified the North Korean special forces using artificial intelligence facial recognition software and that the soldiers have been equipped with Russian uniforms, gear and IDs. Ukrainian officials on Friday sought to bolster Seoul’s claims, releasing video allegedly showing North Korean forces at Russia’s Sergievsky training ground as they prepare for deployment. “We are highly concerned,” White House National Security Council spokesperson Sean Savett told VOA, adding that the U.S. was not able to confirm the South Korean and Ukrainian intelligence assessments. “But if true, this would mark a dangerous development in Russia’s war against Ukraine,” he said. “If the DPRK joins Russia, we will consult with our allies and partners on the implications of such a dramatic move.” The Democratic People’s Republic of Korea, or DPRK, is the official name of North Korea. U.S. and Western officials have for months warned about the budding military ties between Moscow and Pyongyang. This past May, the U.S. Defense Intelligence Agency declassified photos and analysis indicating Russia was using North Korean-made missiles to hit targets in Ukraine, including during an attack on Kharkiv earlier this year. In June, U.S. defense officials also accused Pyongyang of shipping more than 1,000 containers of military equipment and munitions to Russia, possibly in exchange for surface-to-air missile and ballistic missile technology. The latest assessment from South Korea’s intelligence service suggests that such exchanges have accelerated, and that since August of last year, North Korea has sent Russia more than 13,000 containers of artillery rounds, ballistic missiles and anti-tank rockets. The deployment of North Korean troops, though, would appear to be a first. And South Korean officials said the total number of troops going to Russia could grow in the coming weeks and months. Pentagon officials have said previously they were aware of the reports, though they have declined to discuss what information Seoul has shared to this point. “We work with the ROK [Republic of Korea] on a daily basis at both working and strategic levels,” a Pentagon spokesperson told VOA, referring to South Korea by its official name. ”But we will not read out the details of our conversations with them, and we won’t comment on matters of intelligence.” And while the additional troops could make a difference for Russia on the battlefield, U.S. officials argue Moscow’s need for North Korean forces also speaks to its struggles in Ukraine. “Such a move would also indicate a new level of desperation for Russia as it continues to suffer significant casualties on the battlefield in its brutal war against Ukraine,” said the NSC’s Savett. Earlier this month, U.S. officials estimated Russian forces have suffered 600,000 fighters killed or wounded since Moscow launched its invasion of Ukraine in February 2022 — a toll that would surpass the number of Russian casualties in any conflict since World War II. U.S. officials say recent months have been especially costly. “Russia has been averaging more than 1,200 casualties per day,” a U.S. official told VOA on Friday, speaking on the condition of anonymity to discuss intelligence matters. The official said the Russian strategy in eastern Ukraine, and in Kursk in particular, seems to involve “sacrificing its soldiers in desperate attempts to gain territory.”