Kim Jong Un to visit Russia for talks with Vladimir Putin, Kremlin says

A train likely carrying North Korea's leader departed Pyongyang on Monday.

SEOUL and LONDON -- A train presumed to be carrying North Korean leader Kim Jong Un departed Pyongyang on Sunday, beginning its journey to Russia for a planned meeting with President Vladimir Putin, a South Korean official told ABC News.

The leader of the secretive country will pay an official state visit to Russia in the coming days, the Kremlin said on Monday. North Korea's state-run media confirmed the visit.

"Our Dearest Comrade Kim Jong Un will be visiting Russia upon invitation from Russian President Vladimir Putin. During the visit he will meet Putin and hold a summit," the Korean Central News Agency reported Monday.

Putin on Monday began a two-day trip to Vladivostok, a port city near eastern Russia's border with North Korea, where he'll attend an economic forum, Russia's TASS news agency said. Kim's train also appeared to be "heading towards" Vladivostok, the South Korean official said.

He left Pyongyang on Sunday night. The bullet-proof train is expected to cover the 683 miles to Vladivostok in about 20 hours, traveling at a speed of about 37 miles per hour, with a long stopover at the Russia-North Korea border to switch wheels that fit Russian railway tracks.

Discussions "are actively advancing" between Kim and Putin over a possible plan for North Korea to supply weapons to Russia, a U.S. official told ABC News last week.

Such a deal would be "another indication of how desperate Mr. Putin is," said John Kirby, spokesperson for the U.S. National Security Council.

"But if they move ahead, then there will be additional repercussions for North Korea," Kirby said. "The international community and the United States will look for ways to hold them accountable for that."

Kim, who took power in 2011, attended a military parade on Sunday marking the 75th anniversary of the founding of the North Korean state, KCNA reported.

The leader had met on Friday with a delegation visiting North Korea from China, a sit-down with "an atmosphere of deep comradeship," state media said.

ABC News' Ben Gittleson, Shannon K. Crawford, Selina Wang and Tanya Stukalova contributed to this story.