Kim reaches Russia in bulletproof train for cloak-and-dagger talks with Putin

For the first time in four years, North Korean leader Kim Jong Un arrived in Russia on Tuesday for a meeting with President Vladimir Putin that the US claims could result in an arms deal to bolster Moscow's invasion of Ukraine.

Images released by Korean Central News Agency (KCNA) show an unflappable Kim waving from the doors of his green, heavily armoured private train as it left Pyongyang on Sunday night.

Kim and Putin will meet this week in an undisclosed location in Russia's Far East, according to Kremlin spokesman Dmitry Peskov although Putin is presently in Vladivostok for the Eastern Economic Forum.

However, there has been no indication that the internationally isolated pair would hold their talks there.

Experts predict that Moscow will request artillery shells and antitank missiles from North Korea, who in turn are looking for advanced satellite and nuclear-powered submarine technology.

Last week, the White House warned North Korea would "pay a price" if it supplies Russia with weaponry for the conflict in Ukraine, AFP reported.

According to KCNA, Kim left North Korea for Russia on Sunday and was accompanied by top North Korean military officials, including officials in charge of weapons production and space technology.

Peskov said the two leaders would "cooperate on sensitive areas that should not be the subject of public disclosure and announcements".

On Tuesday, Russian news agency Ria Novosti said Kim had crossed the border, with images showing the train with dark green carriages being pulled along a track by a Russian Railways locomotive.