Russian President Vladimir Putin on Monday thanked North Korea for sending troops to fight alongside Russia in Moscow's war against Ukraine and vowed not to forget their sacrifices.

Putin's comments came just hours after North Korea confirmed for the first time that it had deployed troops to fight Ukrainian forces.

Russia said two days earlier that its troops had fully reclaimed the Kursk region, which Ukrainian forces seized last year. Ukrainian officials have denied Russia's claim and said that the operation in certain areas of Kursk is ongoing.

In a statement, Putin praised North Korean troops who he said fought "shoulder to shoulder with Russian fighters, defended our Motherland as their own."

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"The Russian people will never forget the heroism of the DPRK special forces," Putin said. "We will always honor the heroes who gave their lives for Russia, for our common freedom, fighting side by side with their Russian brothers in arms."

Earlier Monday, North Korea's Central Military Commission said the country's leader, Kim Jong Un, had sent troops to Russia to "annihilate and wipe out the Ukrainian neo-Nazi occupiers and liberate the Kursk area in cooperation with the Russian armed forces." North Korean troops eventually made "an important contribution" to Russia seizing the border territory, the commission said.

While this was North Korea's first official confirmation that its troops were deployed to Russia, it has repeatedly expressed its unwavering support of Russia's war against Ukraine.

U.S., South Korean and Ukrainian intelligence officials have said North Korea deployed 10,000-12,000 troops to Russia last fall in its first involvement in a major armed conflict since the Korean War in the early 1950s.

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Putin and Kim said the deployment of North Korean troops was made under a mutual defense treaty signed in June 2024 that requires both countries to use all available means to provide immediate military assistance if either is attacked.

The two U.S. adversaries have moved significantly closer to each other in recent years.

In addition to its deployment of troops, North Korea has been supplying a large number of conventional weapons to Russia. South Korea and the U.S. are concerned that Russia could reward North Korea with military and economic assistance, including by transferring high-tech weapons technologies that can bolster its nuclear weapons program.

Kim citing North Korea’s role in Russia regaining control of the Kursk region suggests his urgent desire to receive what he wants from Russia, including its sensitive military technologies and a solid security commitment to North Korea, according to Moon Seong Mook, an analyst for the Seoul-based Korea Research Institute for National Strategy.

Kremlin spokesman Dmitry Peskov said Monday that Russia could provide military assistance to North Korea if necessary in accordance with the defense treaty, Russian state media reported.

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North Korea and Russia did not disclose how many North Korean soldiers were sent to Russia or how many casualties they suffered. But last month, South Korea’s military assessed that roughly 4,000 North Korean soldiers had been killed or wounded in the Russia-Ukraine war. The South Korean military also said North Korea sent about 3,000 additional troops to Russia earlier this year.

South Korea’s Unification Ministry on Monday called on North Korea to withdraw its troops from Russia immediately, arguing that the North’s support of Russia’s invasion of Ukraine poses a grave provocation to international security. Ministry spokesperson Koo Byoungsam also called the North’s deployment of troops "an act against humanity."

If Russia’s retaking of Kursk is confirmed, it would deprive Ukraine of key leverage in U.S.-brokered efforts to negotiate an end to the war by exchanging its gains for some Russia-occupied land in Ukraine.

U.S. President Donald Trump said Saturday he doubts Putin wants to end the war. Just a day before, Trump had said Ukraine and Russia were "very close to a deal."

The Associated Press contributed to this report.