North Korea is about to increase its support for Russian forces bogged down in Ukraine — with the deployment of several thousand soldiers and military construction personnel near the Ukrainian border.

That’s the report from South Korea’s National Intelligence Service. The forces are the cutting edge of increased cooperation between Moscow and Pyongyang as Russia counts on North Korea for both arms and men in its campaign to take over Ukraine more than three years after Russian troops invaded the country in February 2022.

North Korea’s leader, Kim Jong-un, made the commitment to the secretary of the Russian security council, Sergei Shoigu, when the Russian visited Pyongyang for the first anniversary on June 19 of the signing of a security pact, the NIS said in a briefing for members of the South’s National Assembly.

Although Moscow has been guarded about North Korea’s role in the war, Russia’s deputy prime minister, Marat Khusnullin, said North Korea “wants to join and help with this issue” — restoring the Russian borderline regions, according to the  Russian news agency, Tass. 

Mr. Khusnullin was evasive about details, saying “the timeframe is unclear” and asking, rhetorically, what does it mean that they are ready to arrive?” South Korean reports, however, indicate they are expected to arrive in August.

The Japanese state broadcaster NHK quoted Mr. Shoigu as saying that Mr. Kim had decided to send 6,000 troops to help rebuild the western Russian region of Kursk following cross-border attacks by Ukraine. The force, said NHK, will include 1,000 sappers tasked with removing mines in the Kursk region along Ukraine’s eastern frontier. The remaining 5,000 were described as “military builders” — soldiers — responsible for “reconstruction of roads, communications facilities and other infrastructure.”

Mr. Shoigu, who has previously served as Russia’s defense minister, described the mission as “brotherly aid being sent by the North Korean people and their leader, Kim Jong Un, to our country.” He also said both Russia and North Korea would build memorials honoring North Korea’s sacrifices.

The decision to send in fresh soldiers follows the deployment of more than 10,000 North Korean soldiers to the Kursk region late last year. South Korea’s joint general staff estimates 1,100 of them were killed in the first few months of combat, many by Ukrainian missiles.

The disclosure of plans to send more North Korean troops to Russia contrasts with the secrecy that surrounded the initial deployment. It was only after news of heavy casualties began reaching North Korea that Mr. Kim and his state media machine began publicizing their roles. 

The deal on troops was accompanied by more sweeping plans for relations between Pyongyang and Moscow. So far, however, North Korean forces have not stepped across the Russian border into Ukraine — a move that would mark a major escalation in hostilities.