Kim Jong-un arrives in Russia on 'moving fortress' as he prepares for weapons talks with Vladimir Putin

He was greeted by Russian officials ahead of talks with the country's president which are thought to focus on the war in Ukraine.

The olive green train is is equipped with attack weapons and a helicopter for escape.

The large green locomotive has been used by Kim on many high-profile visits.

The train was notably used during his 2018 trip to Beijing and for a 2019 summit in Hanoi with then-US President Donald Trump.

Kim Jong-un's preferred method of transport mirrors his father Kim Jong Il, who was reportedly scared of flying.

This limited the former leader to making trips accessible only by land, such as to China and Russia.

Kim does not travel abroad frequently, making just seven trips away from his country and twice stepping across the inter-Korean border in his 12 years in power.

Four of those trips were to the North's main political ally, China.

"It will be a fully fledged visit," Kremlin spokesman Dmitry Peskov said.

"There will be negotiations between two delegations, and after that, if necessary, the leaders will continue their communication in a one-on-one format."

US officials, who first said the visit was imminent, said arms talks between Russia and North Korea were actively advancing and that Kim and Putin were likely to discuss providing Russia with weapons for the war in Ukraine.

There has been no confirmation of the site of the summit, but Kim's train passed the junction for Russia's Pacific port of Vladivostok, where Putin was attending a conference, and headed northwards, Japan's Kyodo news and South Korean media reported, saying he might meet Putin at the Vostochny cosmodrome.

Pyongyang and Moscow have denied that North Korea could supply arms to Russia, which has expended vast stocks in more than 18 months of war.

Peskov said Russia's national interests would dictate its policies.