North Korean leader Kim Jong Un stopped in a far eastern Russian city on Friday to see a factory that builds the country’s most advanced fighter jets.

It came on Mr Kim’s extended trip that hints at his interest in sophisticated weaponry, as the US and others warned Moscow and Pyongyang against making banned weapons transfer deals.

Mr Kim’s visits to Russian weapons and technology sites and meetings with president Vladimir Putin have raised speculation he will supply ammunition to Russia for its war efforts in Ukraine in exchange for receiving advanced weapons or technology from Russia.

It comes as the two nations deepen their ties while both are increasingly isolated and sanctioned in separate confrontations with the West.

Russia’s state news agency RIA Novosti published video showing Mr Kim’s armoured train pulling into a station in the city of Komsomolsk-on-Amur and Mr Kim’s convoy sweeping out of the station shortly afterward.

TASS news agency said Mr Kim and local Russian officials were headed for a plant that produces Su-35 and Su-57 fighter jets.

Mr Kim is to travel next to Vladivostok to view Russia’s Pacific fleet, a university and other facilities, Mr Putin told Russian media after his summit with Mr Kim.

Experts say in return for helping Mr Putin replenish war supplies, Mr Kim would seek Russian help to modernise his air force and navy, which are inferior to those of rival South Korea while Mr Kim has devoted much of his own resources to his nuclear weapons programme.

The summit between Mr Kim and Mr Putin this week took place at the Vostochny Cosmodrome, Russia’s most important domestic launch centre.

North Korea has struggled to put into space an operational spy satellite to monitor US and South Korean military movements.

Asked whether Russia will help North Korea obtain satellites, Russian state media said Mr Putin responded: “That’s why we have come here. (Mr Kim) shows keen interest in rocket technology. They’re trying to develop space, too.”

Mr Putin, for his part, would want to receive ammunition, artillery shells and even ballistic missiles from North Korea to replenish his exhausted arms inventory in the second year of Russia’s war in Ukraine, foreign experts say.

Since last year, the US accused North Korea of providing ammunition, artillery shells and rockets to Russia, likely much of them copies of Soviet-era munitions.

South Korean officials said North Korean weapons provided to Russia have already been used in Ukraine.

On Thursday evening, the national security advisers of the US, South Korea and Japan talked by phone and expressed “serious concerns” about prospective weapons deals between Russia and North Korea.

They warned Russia and North Korea would “pay a clear price” if they go ahead with such deals, according to South Korea’s presidential office.

The White House said the three national security advisers noted that any arms export from North Korea to Russia would directly violate multiple UN Security Council resolutions, including resolutions that Russia, a permanent member of the UN council, itself voted to adopt.