"The intelligence authorities believe the train presumed to be carrying Kim Jong-Un is moving to Vladivostok," a South Korean official told Yonhap News Agency.

Another senior official confirmed to the South Korean news agency that Kim Jong Un appears to have departed Pyongyang and is headed to Russia.

Meanwhile, the Russian government has confirmed that Kim Jong Un will visit Moscow at the invitation of Vladimir Putin.

"At the invitation of Russian President Vladimir Putin, Chairman of State Affairs of the Democratic People’s Republic of Korea Kim Jong-un will pay an official visit to the Russian Federation in the coming days," the Kremlin said in a statement as quoted by Sputnik Globe.

However, the exact date of the visit or whether a meeting with Putin is planned has not been specified in the statement.

The two leaders are likely to discuss the possibility of North Korea supplying weapons to Moscow to support the ongoing war in Ukraine.

A U.S. official earlier told CBS News that the North Korean leader will discuss the possibility of his nation supplying weapons to Moscow to support its war against Ukraine.

US National Security Council spokesman John Kirby told reporters recently as quoted by CBS News that Russia's Defence Minister, Sergei Shoigu, recently travelled to North Korea to "try to convince Pyongyang to send artillery ammunition" to Russia, and after the visit, Putin and Kim exchanged letters "pledging to increase their bilateral cooperation."

According to reports, Kim Jong Un and Putin last met in April 2019 in Vladivostok.