North Korea and the Russian-backed separatist Donetsk region of Ukraine will develop "equally beneficial bilateral cooperation", Donetsk leader Denis Pushilin said in a letter to Kim Jong Un, North Korean state media reported on Wednesday.

In July, North Korea recognised the Donetsk (DPR) and Luhansk People's Republics (LPR) in eastern Ukraine's Donbas region, as independent states.

The move made North Korea only the third country after Russia and Syria to recognise the two breakaway entities.

Ukraine immediately severed relations with Pyongyang over the move.

Pushilin wrote a letter to congratulate Kim on the August 15 Korean liberation day, state news agency KCNA reported, two days after reporting a similar message from Russian President Vladimir Putin to Kim.

"The people of the Donbas region, too, are fighting to regain their freedom and justice of history today just as the Korean people did 77 years ago," the report cited Pushilin's letter as saying.

"The message expressed the conviction that an equally beneficial bilateral cooperation agreeing with the interests of the peoples of the two countries will be achieved between the People's Republic of Donetsk and the Democratic People's Republic of Korea," KCNA added, using the official name of North Korea.

Russia justified its decision to launch the war, which it calls a "special military operation", by saying it was protecting Russian speakers who live there from "genocide". Ukraine accuses Russia of waging an imperial-style war of conquest.

Pushilin has previously said he hoped for "fruitful cooperation" and increased trade with North Korea, and officials from North Korea, Russia, and the breakaway regions have discussed eventually sending North Korean labourers.

A 2017 U.N. Security Council resolution, which Russia backed, demanded that all countries repatriate all North Korean workers by December 2019 to stop them earning foreign currency for North Korea's nuclear and ballistic missile programs.