Russian President Vladimir Putin has written to North Korean leader Kim Jong Un, to suggest the two countries form closer ties.
North Korea's state media, KCNA, said the letter from Mr Putin had suggested the pair work to "expand the comprehensive and constructive bilateral relations with common efforts".
Delivered to Pyongyang on North Korea's liberation day, it went on to say a union would help "strengthen the security and stability of the Korean peninsula and the Northeastern Asian region".
In a separate letter in reply, Mr Kim said that since a Russian-North Korean friendship had been forged in World War II with victory over Japan, the "strategic and tactical cooperation, support and solidarity" between the two countries had reached a new level.
Their common efforts to frustrate threats and provocations from "hostile military forces", it said, bound them.
KCNA did not identify the "hostile forces", but it has typically used that term to refer to the US and its
In July, Mr Kim said North Korea was ready to mobilise its nuclear war deterrent "accurately and promptly" in the face of potential military conflicts with the US or South Korea.
Also in July, North Korea 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 has been resisting a Russian invasion since February - described by Moscow as a "special military operation"- immediately severed relations with Pyongyang over the move.