NATO Secretary General Mark Rutte confirmed on Monday that North Korean troops have been sent to help Russia in its war against Ukraine, representing the "growing desperation" of Russian President Vladimir Putin.

Rutte told reporters that increasing military cooperation between Russia and North Korea "is a threat" to Indo-Pacific and Euro-Atlantic security.

"Today, I can confirm that North Korean troops have been sent to Russia, and that North Korean military units have been deployed to the Kursk region," NATO Secretary-General Mark Rutte told reporters.

Russia is currently fighting back against a Ukrainian incursion into the Kursk region.

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North Korean soldiers marching

North Korean soldiers march in a parade for the 70th anniversary of North Korea's founding day in Pyongyang, North Korea, on Sept. 9, 2018. (AP Photo/Ng Han Guan, File)

Rutte said the addition of North Korean troops in the conflict represents "a significant escalation" in and marks "a dangerous expansion" of "Russia’s illegal war."

North Koreas leader Kim Jong Un and Russian President Vladimir Putin

North Korean leader Kim Jong Un, left, and Russian President Vladimir Putin smile during their meeting at the Pyongyang Sunan International Airport outside Pyongyang, North Korea, on June 19, 2024.  (Gavriil Grigorov, Sputnik, Kremlin Pool Photo via AP, File)

"Over 600,000 Russian soldiers have been killed or wounded in Putin’s war and he is unable to sustain his assault on Ukraine without foreign support," Rutte said.

U.S. Defense Secretary Lloyd Austin confirmed the troop movement Wednesday in a statement, saying it would be a "a very, very serious issue" if North Korean troops deploy to Ukraine. 

The Kremlin has dismissed reports of North Korea deploying troops as "fake news," while a North Korean United Nations representative called the reports "groundless rumors," Reuters reported. 

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Rutte spoke in Brussels after a high-level South Korean delegation, including top intelligence and military officials as well as senior diplomats, briefed the alliance’s 32 national ambassadors at NATO headquarters.

NATO Secretary General Mark Rutte

NATO Secretary General Mark Rutte confirmed that North Korean troops have been sent to help Russia in its war against Ukraine. (AP Photo/Virginia Mayo)

Rutte said NATO is "actively consulting within the alliance, with Ukraine, and with our Indo-Pacific partners," on developments.

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"We continue to monitor the situation closely," he said. He did not take questions after the statement.

The Associated Press contributed to this report.