Pyongyang, North Korea - North Korea said Monday that leader Kim Jong Un would visit Russia and meet President Vladimir Putin, with the reclusive leader's armored train reportedly on its way to the border.

Experts suggest that Putin is seeking artillery shells and antitank missiles from North Korea for Moscow's war in Ukraine, while Kim is reportedly in search of advanced technology for satellites and nuclear-powered submarines, as well as food aid for his impoverished nation.

Kim "will soon visit the Russian Federation at the invitation of ... Putin," the North's official Korean Central News Agency said.

"The respected Comrade Kim Jong Un will meet and have a talk with Comrade Putin during the visit," it added.

The Kremlin also confirmed Monday that Kim would visit Russia "in the coming days."

The announcement ends days of speculation after US and other officials told The New York Times at the weekend that Kim, who rarely leaves North Korea, was likely to head by armored train to Vladivostok for arms talks with Putin.

Kim has not traveled outside North Korea since the start of the coronavirus pandemic.

South Korea's Yonhap news agency quoted an unidentified official as saying "intelligence authorities believe the train presumed to be carrying Kim Jong-un is moving to Vladivostok."

Broadcaster YTN said Seoul "expects that Chairman Kim will hold a meeting with President Putin of Russia around the day after tomorrow," meaning Wednesday.

Moscow, a historical ally of Pyongyang, was a crucial backer of the isolated country for decades, and their ties go back to the founding of North Korea 75 years ago.

Kim has been steadfast in his support for Moscow's invasion of Ukraine, including, Washington says, supplying rockets and missiles.

In July, Putin hailed Pyongyang's "firm support for special military operations against Ukraine."

Vladivostok will be hosting the Eastern Economic Forum until Wednesday.

The White House warned last week that Pyongyang would "pay a price" if it supplies Moscow with weaponry for its war in Ukraine.

Washington said Russia could use weapons from North Korea to attack Ukrainian food supplies and heating infrastructure heading into winter to "try to conquer territory that belongs to another sovereign nation."

Andrei Lankov, a North Korea expert at Kookmin University in Seoul, told AFP that a Putin-Kim summit was part of "gentle diplomatic blackmail" by Moscow of Seoul because Russia did not want South Korea to supply weapons to Kyiv.

Seoul is a major arms exporter and has sold tanks to Kyiv's ally Poland, but longstanding domestic policy bars it from selling weapons into active conflicts.

"The major worry of the Russian government now is a possible shipment of the South Korean ammunition to Ukraine, not just one shipment but a lot of shipments," Lankov said.