North Korean leader Kim Jong Un has arrived in Russia on his private train ahead of his meeting with President Vladimir Putin as concerns grow over a possible arms deal between Pyongyang and Moscow.

Meanwhile, the Kremlin has said the two leaders will meet in 'Russia’s Far East'.

"We are not telling yet [where talks will take place]. In the Far East," Kremlin Spokesman Dmitry Peskov was quoted as saying by Tass, adding that the talks will be held between the two delegations as well as in a one-on-one format, followed by an official dinner.

Meanwhile, the US warned it would 'aggressively' enforce existing sanctions and add new ones if North Korea supplies arms to Russia for its ongoing war against Ukraine.

"I will remind both countries that any transfer of arms from North Korea to Russia would be in violation of multiple United Nations Security Council resolutions," US State Department spokesperson Matthew Miller told reporters.

"We, of course, have aggressively enforced our sanctions against entities that fund Russia’s war effort, and we will continue to enforce those sanctions and will not hesitate to impose new sanctions if appropriate," he said.

The US official, however, did not specify whether the sanctions will be imposed against one of the nations or both.

Miller said: "I think I want to wait and see what the outcome of the meeting is before speculating, but we have always looked to impose sanctions and hold accountable countries or entities – entities that fund Russia’s war effort."

Speaking on Russian President Vladimir Putin and the ongoing war in Ukraine, he said: "A year and a half ago President Putin launched this war against Ukraine with its full-scale aggression with a dream of restoring the glory of the Russian empire. That hope, that expectation of his, has failed."

He said: "It will continue to fail. And I think there’s no better evidence of that than now, a year and a half later, not only has he failed to achieve his goals on the battlefield, but you see him travelling across his own country hat in hand to beg Kim Jong-un for military assistance."

He argued that Putin seems to be having trouble in sustaining the military effort so he is looking for help from North Korea.