Intelligence agencies on three continents have assessed that North Korean soldiers quietly entered Russia as the country seeks more manpower in its deadlocked war of aggression against Ukraine. Last Friday, House Permanent Select Committee on Intelligence Chairman Mike Turner wrote a letter to President Joe Biden calling for “an immediate classified briefing … concerning the possible engagement of North Korean troops in a potentially escalating and broadening Ukrainian conflict.”

According to South Korean intelligence, the first North Korean soldiers arrived on Russian ships in the east Russian port city of Vladivostok between October 8 and 13. There, they received Russian uniforms, weapons, and fake IDs. South Korea estimated that at least 1,500 North Korean soldiers had arrived, with more on the way.

“They are not wearing their own uniforms, instead disguising themselves in Russian uniforms, having no operational control but just following Russian orders,” South Korean Defense Minister Kim Yong-hyun said Thursday.

South Korea said the troops were part of North Korea’s special operations force, although other experts suggest, based on the slight and short build of some soldiers seen in photographs, that they may not be the country’s crack troops.

When asked about the presence of North Korean troops, Russian leader Vladimir Putin answered coyly, saying merely that his country was “in contact” with Pyongyang. “We have never doubted that the North Korean leadership takes our agreements seriously. But what and how we will do is our business,” he insisted. For their part, North Korean state-controlled media has also stayed quiet about the semi-secret move.

On Thursday, Ukrainian intelligence announced that some North Korean soldiers had been spotted in the western Russian region of Kursk, where Russia has struggled to push back a Ukrainian counter-attack due to a lack of manpower. Ukraine estimated that roughly 12,000 North Korean troops have entered Russia, including 500 officers and three generals, and that they are receiving training at five military sites in eastern Russia.

U.S. intelligence has also collected evidence of the presence of North Korean troops in Russia, Defense Secretary Lloyd Austin confirmed Wednesday, although the U.S. estimate was 3,000 soldiers, only a quarter of the number estimated by Ukraine.

Thus far, however, “What exactly they are doing is left to be seen,” Austin added. “We will continue to pull this thread and see what happens here. If they’re co-belligerents — [if] their intention is to participate in this war on Russia’s behalf — that is a very, very serious issue.”

The other possibility is that North Korean forces are in Russia for joint military training exercises, given the two countries’ close military alliance. However, if that were the case, there would be no obvious reason for secrecy.

If the North Korean soldiers are intended to fight against Ukraine, it would be “an indication that [Putin] may be [in even] more trouble than most people realize,” Austin added.

U.S. officials estimate that Russia has suffered 300,000 casualties in its war against Ukraine — largely a consequence of Western munitions supplied to Ukraine. After burning through Russia’s domestic supply of available conscripts, Putin may be turning to his totalitarian allies to supply further assistance.

At least, this is the perspective of South Korea’s Defense Minister Kim, who told South Korean lawmakers on Thursday, “North Korea is not sending troops but rather cannon-fodder mercenaries.”

At first glance, North Korea may seem like a strange choice for Russia to recruit extra bodies to feed its bloodthirsty war. However, despite its small population and economy, North Korea maintains the world’s fourth-largest active-duty military, with nearly 1.3 million soldiers, not counting another 5.9 million reserves. Its male conscripts are required to serve for eight to 10 years and female conscripts for five years. South Korea estimates its armaments at 4,300 tanks, 8,800 artillery pieces, 810 fighter planes, and 70 submarines.

Because of this over-investment in the military — and its totalitarian dictatorship — the tiny pariah state has a poor economy. North Korea has too many soldiers, and it needs cash. So, renting its army out to fight in Russia’s war serves the regime’s interests, even while it fails to take into consideration the value of its own subjects’ lives.

Now that North Korean troops have been spotted in western Russia, they could arrive on the battlefield soon. Dutch Defense Minister Ruben Brekelmans predicted that the North Koreans “will probably first be deployed in Kursk,” according to intelligence reports. According to Ukrainian intelligence, “the first North Korean military will be used by Russia in combat zones” between Sunday and Monday.

If North Korean soldiers do engage in hostilities with Ukraine, it could have international implications, both in Ukraine and in the Indo-Pacific region, said Austin. South Korea is watching its northern counterpart’s actions closely.

On this point, Turner and Austin agree. “These troop movements, if true, are alarming and are an extreme escalation of the conflict in Ukraine. They require an immediate response from the United States and our NATO allies to avoid a widening conflict,” Turner told President Biden. “North Korean troops, either attacking Ukraine from Russian territory or entering into Ukrainian territory, must be a red line for the United States and NATO. Your administration must make that absolutely clear and unequivocal.”