Pyongyang, North Korea - Russia's President Vladimir Putin hailed North Korean troops sent to fight in Ukraine as "heroic" in a letter to Kim Jong Un, North Korean state media reported Friday.

In a letter marking the anniversary of Korea's liberation from Japanese rule, Putin recalled how Soviet Red Army units and North Korean forces fought together to end Japan's colonial occupation.

"The bonds of militant friendship, goodwill and mutual aid which were consolidated in the days of the war long ago remain solid and reliable even today," Putin said in a letter revealed by North Korean state media.

"This was fully proved by the heroic participation of the DPRK soldiers in liberating the territory of Kursk Region from the Ukrainian occupationists," he said, according to news agency KCNA.

Russia Russia takes alarming action against Reporters Without Borders

Russia Kremlin issues update on timing of Trump-Putin meeting as Zelensky demands talks

"The Russian people will keep forever the memories of their bravery and self-sacrifice."

Putin added that the two countries would continue to "act jointly and effectively defend their sovereignty and make a significant contribution to establishing a just and multi-polarized world order."

Russia and North Korea have been forging increasingly closer ties, with the two countries signing a mutual defense pact last year, when Putin visited the reclusive state.

In April, North Korea confirmed for the first time that it had deployed a contingent of its soldiers to the front line in Ukraine, alongside Russian troops.

South Korean and Western intelligence agencies have said Pyongyang sent more than 10,000 soldiers to Russia's Kursk region in 2024, along with artillery shells, missiles, and long-range rocket systems.

Around 600 North Korean soldiers have been killed and thousands more wounded fighting for Russia, Seoul has said.

The letter from Putin came alongside a visit by a Russian delegation to Pyongyang, where the speaker of the Duma thanked Kim for sending "excellent soldiers" to Ukraine, KCNA reported.

Vyacheslav Volodin's delegation arrived Thursday and was received by a military honor guard for a visit marking "the 80th anniversary of Korea's liberation."

Volodin thanked Kim for "dispatching excellent soldiers to the Kursk liberation operations for driving out the Ukrainian aggressors," according to KCNA.

Russia Putin hails Trump administration's "sincere" efforts to end Ukraine war ahead of Alaska talks

Russia Putin and US envoy Witkoff hold "constructive" talks ahead of sanctions deadline

He added that Russia would never forget the North Korean troops "who fought at the cost of their lives in Russia."

Kim, meanwhile, said the delegation's visit would promote the "development of the DPRK-Russia relations already on a new level."

He also mentioned that he had a phone call with Putin two days ago, agreeing to expanded bilateral cooperation and "closer contact and communication between the state leaderships."

The call came three days ahead of Friday's summit between Putin and Trump, the first between a sitting US and Russian president since 2021, as Trump seeks to broker an end to Russia's more than three-year war in Ukraine.