The South Korean TV channel YTN reports.
"The intelligence authorities believe the train presumed to be carrying Kim Jong-Un is moving to Vladivostok," said a South Korean official.
Another senior official confirmed that Kim Jong Un has left Pyongyang and is heading to Russia.
In addition, on the same day, Russian media reported that the Russian president had arrived in Vladivostok, where he would take part in the Eastern Economic Forum.
Subsequently, the Kremlin confirmed Kim Jong Un's visit to Russia "in the coming days," noting that the DPRK leader was traveling at Putin's invitation.
Earlier, White House spokesman John Kirby said that talks between Russia and the DPRK on military cooperation are "actively progressing."
In July, Russian Defense Minister Sergei Shoigu visited the DPRK and met, among others, with his North Korean counterpart.
In early August, the White House accused Russia of trying to buy ammunition from the DPRK.
On August 18, US President Joe Biden was ready to meet with North Korean leader Kim Jong Un "without preconditions" to discuss the denuclearization of the Korean Peninsula.
On August 31, the United States imposed sanctions on two Russian citizens over the development of weapons of mass destruction and ballistic missiles for the DPRK.
On September 4, The New York Times reported, citing US and allied officials, that North Korean leader Kim Jong Un plans to visit Russia in September and meet with Vladimir Putin to discuss military cooperation.
On the evening of Friday, September 8, at a parade in honor of the 75th anniversary of the state's founding, DPRK leader Kim Jong Un met with a Chinese delegation before his trip to Russia next week.
Oleksandr Kovalenko, a military and political observer at the Information Resistance group, believes that North Korea will not start supplying weapons to Russia without coordinating it with China.