Pyongyang, North Korea - North Korea sent troops to clear mines in Russia's Kursk region earlier this year, leader Kim Jong-un publicly acknowledged in a speech carried on Saturday by state media.

Pyongyang has sent thousands of troops to fight for Moscow as it presses ahead with its years-long invasion of Ukraine, according to South Korean and Western intelligence agencies.

Analysts say Russia is giving North Korea financial aid, military technology, food and energy supplies in return, allowing the diplomatically isolated nation to sidestep tough international sanctions on its nuclear and missile programs.

Hailing the return of an engineering regiment, Kim noted that they wrote "letters to their hometowns and villages at breaks of the mine-clearing hours", according to the Korean Central News Agency.

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The regiment suffered the "heartrending loss of nine lives" during the 120-day deployment that started in August, Kim said in a speech at a welcome ceremony on Friday, KCNA reported.

He awarded the deceased soldiers state honors, and said: "All of you, both officers and soldiers, displayed mass heroism overcoming unimaginable mental and physical burdens almost every day."

The troops had been able to "work a miracle of turning a vast area of danger zone into a safe and secure one in a matter of less than three months."

North Korea only confirmed in April that it had deployed troops to support Russia and that its soldiers had been killed in combat.

Images released by KCNA showed a smiling Kim embracing returned soldiers, some in wheelchairs, at the grand ceremony in Pyongyang on Friday.