Pyongyang, North Korea - North Korea's Supreme Leader Kim Jong-un urged his military to be ready "for real war" as he observed a firing contest of artillery units, Pyongyang's state media reported on Thursday.

Kim's remarks follow North Korea's decision to send troops to fight on the Ukrainian frontline, a move that was reinforced earlier in July when Russian Foreign Minister Sergei Lavrov visited Pyongyang.

Video footage aired by state-run Korea Central Television on Thursday showed soldiers from artillery units firing shells towards the sea. Kim is seen looking through binoculars at an observation post, flanked by two military officials.

He urged North Korea's soldiers to be ready "for real war" at "anytime" and be capable of "destroying the enemy in every battle," the Korean Central News Agency reported in an English dispatch.

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South Korean and Western intelligence agencies have reported that Pyongyang sent more than 10,000 soldiers to Russia's Kursk region last year, 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 two heavily sanctioned nations signed a military treaty last year, including a mutual defense clause, during a rare visit to Pyongyang by Russian President Vladimir Putin.

According to KCNA, the treaty functions as a "legal framework for realizing the far-reaching plan of the state leadership of the two countries."