Kim's tour comes days after South Korea's spy agency said Pyongyang had sent a "large-scale" troop deployment to Russia to fight against Ukraine, cementing Pyongyang's contentious military alliance with Moscow.

Kim "examined the readiness for action of strategic deterrence directly connected with the security of the country", the official Korean Central News Agency (KCNA) reported.

Images in state media showed Kim -- wearing his customary black leather jacket -- standing in front of massive Hwasong-18 solid-fuel intercontinental ballistic missiles.

He was also pictured next to medium- to long-range hypersonic missiles, which are difficult to intercept due to their irregular flight paths.

Kim inspected "important functions and capabilities of launch-related facilities in the missile bases", KCNA said.

Kim hailed the country's missile force for its "pivotal role" in the country's war deterrence, saying it was a top priority.

He was accompanied by his powerful sister Kim Yo Jong and other military officials, according to KCNA.

- 'Increasing threats' -

"The U.S. strategic nuclear means pose ever-increasing threats to the security environment of the Democratic People's Republic of Korea," KCNA quoted Kim as saying.

As a result, it is crucial that "the DPRK more definitely bolsters its war deterrence and takes a thorough and strict counteraction posture of the nuclear forces".

KCNA added that Kim "stressed the need to further modernize and fortify the strategic missile bases".

This week South Korea's spy agency released satellite images it said showed that 1,500 elite special forces soldiers from North Korea training in Russia ahead of deployment to the front line of the war against Ukraine.

The US and NATO have yet to confirm the deployment -- which both Pyongyang and Moscow have denied.

Ukraine media reported President Volodymyr Zelensky saying Tuesday that two North Korean brigades -- with up to 6,000 personnel each -- were undergoing training in Russia.

Also on Tuesday, the Russian Telegram channel Astra released clips purportedly showing Russian and North Korean soldiers, with audio capturing phrases such as "I'm tired" and "we're late" spoken in a North Korean accent.