North Korean leader Kim Jong-un has sent a congratulatory message to Russian President Vladimir Putin over Victory Day, expressing his "firm support and solidarity" with Moscow, state media reported Thursday.

Kim extended his "warm congratulations and comradely greetings" to Putin in the message celebrating the 79th anniversary of the Soviet Union's World War II victory over Nazi Germany, according to the Korean Central News Agency.

Kim touted Putin as leading efforts to defend Russia's sovereignty against "vicious challenges and threats of the hostile forces," apparently pointing to Moscow's war with Ukraine.

"I express firm support and solidarity with the sacred cause of Russia, hoping that you and the brave Russian army and people would win fresh victory in the struggle to defeat the imperialists' hegemonic policy," Kim was quoted as saying by the KCNA.

Earlier this week, the North Korean leader sent a congratulatory message to Putin for formally starting his fifth term as Moscow's leader. Putin began his fifth term Tuesday, extending his 24-year rule for another six years after a landslide victory in the March election.

North Korea and Russia have been deepening military cooperation and bolstering bilateral ties after Kim and Putin held the summit in September last year.

Seoul's unification ministry said Kim has sent a Victory Day congratulatory message to Putin for the third straight year since Russia's war with Ukraine in 2022. Previously, the North did so only on Russia's anniversaries whose final numbers end in a five or zero.

"North Korea appears to be trying to show off its close ties with Russia and creating the atmosphere (to prepare for) Putin's trip to North Korea," a ministry official told reporters on condition of anonymity.

The Kremlin earlier said Putin had accepted Kim's invitation to visit North Korea during the summit held at Russia's Vostochny spaceport. (Yonhap)