Vladivostok, Russia - North Korean leader Kim Jong-un arrived in Russia ahead of a meeting with Russian President Vladimir Putin, according to South Korea's Defense Ministry.

There were indications that Kim's private armored train had crossed the border into Russia on Tuesday morning, the Defence Ministry in Seoul said.

Kremlin spokesperson Dmitry Peskov said Putin's meeting with Kim would take place in Russia's Far East, Russian state news agency TASS reported, though it wasn't initially clear exactly where the meeting would take place.

Peskov said there would be meetings between the two delegations and one-on-one talks before an official dinner.

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North Korean state media earlier had confirmed that Kim set off for Russia from Pyongyang by train on Sunday afternoon. The Kremlin confirmed the planned meeting between Kim and Putin in the Russian city of Vladivostok on Russia's Pacific coast, which had been reported by the New York Times last week.

Moscow is concerned with securing supplies of weapons and ammunition for its war against Ukraine, the newspaper reported, citing unnamed officials from the US and allied governments.

The newspaper said Putin is hoping for North Korean artillery shells and anti-tank weapons, while Kim is said to be hoping for advanced technology for satellites and nuclear-powered submarines, as well as food aid.

Following confirmation of the meeting, the US State Department said Washington reserves the right to impose further sanctions on Russia and North Korea given the planned talks on arms deliveries.

"Any transfer of arms from North Korea to Russia would be a violation of multiple UN Security Council resolutions," State Department spokesperson Matthew Miller said on Monday.

"The fact that Russia is having to beg North Korea for military support speaks to the effectiveness of our sanctions and our export controls, that they have been denied the weapons they need and the raw materials they need to sustain this war," he said, referring to Russia's full-scale invasion of Ukraine launched in February 2022.

"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 [this] as him begging for assistance," Miller added.