North Korea’s leader, Kim Jong-un, inspected nuclear-capable strategic bombers in Russia on Saturday, according to Russian state media, as he continued a trip that has raised fears of the two nations deepening their military ties against a common enemy, the United States.

Mr. Kim arrived in Primorsky Krai, in Russia’s Far East, on Saturday morning traveling via his armored train. There, Sergei K. Shoigu, the defense minister, and other top Russian military officers showed him Russia’s hypersonic Kinzhal missile mounted on a MIG-31 jet, as well as three other key elements of Russia’s nuclear force: the Tu-95MS turboprop strategic bomber and Tu-160 and Tu-22M3 supersonic bombers, according to RIA Novosti, a Russian news outlet.

When Mr. Shoigu visited Pyongyang in July, Mr. Kim took him to an exhibition of missiles and other weapons, raising fears that Russia was turning to North Korea for ammunition badly needed in its war against Ukraine. United States officials have repeatedly warned that North Korea was already shipping artillery shells and army rockets to Russia and that in return it wanted Russian technology to advance its own military capabilities.

The prospect of such military exchanges presents a double challenge for Washington: Conventional weapons from North Korea could help Moscow prolong its invasion of Ukraine, while technical help from Russia would expand the North’s nuclear threat against the United States and its allies in the region, South Korea and Japan.

Mr. Kim’s visit to Russia this week has deepened these concerns. A meeting with President Vladimir. V. Putin on Wednesday at the Vostochny Cosmodrome provided Mr. Putin a chance to show off his country’s satellite and rocket technologies. Two days later, Mr. Kim visited Komsomolsk-on-Amur, where he went to a fighter jet factory.

On Saturday, in addition to the airfield in Artyom, Primorsky Krai, Mr. Kim was expected to visit the port at nearby Vladivostok to view Russia’s far eastern naval fleet, which includes nuclear submarines.

The whistle-stop tour highlighted the kind of advanced military technologies Mr. Kim covets for his country.

Strengthening North Korea’s military has been Mr. Kim’s top priority since he came to power in 2011 after the death of his father, Kim Jong-il. Under the current Mr. Kim, the North has conducted nuclear and intercontinental ballistic missile tests, as well as developing other missiles it said were designed to carry nuclear warheads.

But the country has faced technical setbacks in its nuclear and missile programs.

North Korea has never launched an ICBM on an intercontinental range, raising doubts about whether it can. Since 2021, it has been testing what it has called its first hypersonic missile, yet South Korean officials say a truly hypersonic missile is still years away. And North Korea has tried twice in recent months to put into orbit what would be its first military spy satellite, failing both times when its carrier vehicles malfunctioned.

Mr. Kim has said he wanted to build a nuclear-propelled submarine. But it took his country years to unveil what it called its first submarine capable of firing nuclear missiles. The North created the sub by retrofitting a ballistic missile launch deck to an old Soviet-era diesel-powered submarine. When the sub was launched this month, South Korea expressed doubt that it could function normally.