SEOUL, Aug 15 (Reuters) - Russian President Vladimir Putin told North Korean leader Kim Jong Un the two countries will "expand the comprehensive and constructive bilateral relations with common efforts," Pyongyang's state media reported on Monday.

In a letter to Kim for Korea's liberation day, Putin said closer ties would be in both countries' interests, and would help strengthen the security and stability of the Korean peninsula and the Northeastern Asian region, North Korea's KCNA news agency said.

Kim also sent a letter to Putin saying Russian-North Korean friendship had been forged in World War II with victory over Japan, which had occupied the Korean peninsula.

The "strategic and tactical cooperation, support and solidarity" between the two countries has since reached a new level is their common efforts to frustrate threats and provocations from hostile military forces, Kim said in the letter. KCNA did not identify the hostile forces, but it has typically used that term to refer to the United States and its allies.

Kim predicted cooperation between Russia and North Korea would grow based on an agreement signed in 2019 when he met with Putin.

North Korea in July recognised two Russian-backed breakaway "people's republics" in eastern Ukraine as independent states, and officials raised the prospect of North Korean workers being sent to the areas to help in construction and other labour.

Ukraine, which is resisting a Russian invasion described by Moscow as a "special military operation", immediately severed relations with Pyongyang over the move.