Such units are among the thousands of troops that South Korea's spy agency says Pyongyang has deployed to Russia to support Moscow's war against Ukraine.

During the visit to a special operations unit on Friday, Kim said the "actual war capability for guaranteeing victory in the war field is bolstered up through intensive training," the Korean Central News Agency (KCNA) reported.

He added that their training is "the most vivid expression of patriotism and loyalty to the country," according to the agency.

Images released by state media showed Kim peering through the scope of a sniper rifle that KCNA said was going to be "newly supplied to special operation units".

Other images showed him pointing to the bullseye of a target, crouching alongside heavily camouflaged soldiers, and smiling and waving to troops.

Kim supervised "automatic rifle firing drills and sniper rifle firing drills" and, after personally test-firing the weapon, expressed "great satisfaction over the performance and power of the sniper rifle developed in our own way", KCNA said.

Kim's visit to the special forces came on the same day that South Korea's Constitutional Court upheld president Yoon Suk Yeol's impeachment over his disastrous martial law declaration, booting him from office and triggering fresh elections.

Yoon had defended his December 3 attempt to subvert civilian rule as necessary to root out "anti-state forces" and what he claimed were threats from North Korea.

KCNA reported Yoon's dismissal for the first time on Saturday, citing foreign media.

South Korea's opposition leader Lee Jae-myung is seen as a frontrunner in the next election, experts say, and his party has taken a more conciliatory approach towards North Korea.

US President Donald Trump, who met Kim three times during his first administration, said this week that he is in "communication" with Kim and intends to "do something at some point", according to Seoul's Yonhap news agency.