North Korean leader Kim Jong Un arrived in Russia on Tuesday, South Korea's military and Russian state media said, where he is expected to hold a highly anticipated meeting with President Vladimir Putin.

"The Ministry of National Defense believes that North Korea's Kim Jong Un entered Russia early this morning using a private train," Seoul said.

Kim boarded his personal armored train in Pyongyang on Sunday, according to the state-run Korean Central News Agency.

He was reportedly joined by unspecified members of the ruling party and military. He left his train to meet local officials at the Russian border station of Khasan, reported Reuters news agency. 

Russia's RIA Novosti news agency later shared photos claiming to show Kim's dark green train carriages being pulled by a Russian Railways locomotive in the Primorsky region.

What's on the agenda?

The meeting would be Kim's first foreign trip since the COVID-19 pandemic, which forced the hermit state to tighten its border restrictions even further.

One possible venue could be the city of Vladivostok in Russia's Far East. Putin arrived in Vladivostok on Monday to attend the Eastern Economic Forum that runs through Wednesday.

Analysts, as well as US officials, believe the meeting could be a chance for Putin to request artillery shells and antitank missiles from North Korea to be used against Ukraine.

"Having to travel across the length of his own country to meet with an international pariah to ask for assistance in a war that he expected to win in the opening month, I would characterize it as him begging for assistance," US State Department spokesman Matthew Miller told reporters.

In return, Kim is reportedly seeking advanced technology for satellites and nuclear-powered submarines, as well as food aid for his impoverished nation.

Kremlin spokesperson Dmitry Peskov said that Putin and Kim could hold one-on-one meetings if necessary.

"As you know, while implementing our relations with our neighbors, including North Korea, the interests of our two countries are important to us, and not warnings from Washington," he said.

"It is the interests of our two countries that we will focus on."

zc/wd (AP, AFP, Reuters)