Pyongyang has sent thousands of troops to fight for Moscow as it presses ahead with its nearly four-year 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 programmes.

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 (KCNA).

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 honours to “add eternal lustre” to their bravery.

“All of you, both officers and soldiers, displayed mass heroism overcoming unimaginable mental and physical burdens almost every day,” Kim said.

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.