Washington DC - Russian President Vladimir Putin's visit to North Korea is cause for great concern, the US government said on Tuesday.

"The deepening cooperation between Russia and the DPRK is something that should be of concern," US Department of Defense spokesman Pat Ryder said in Washington, using the acronym of the Democratic People's Republic of Korea.

"Especially to anyone that's interested in maintaining peace and stability on the Korean peninsula, but also supporting the people of Ukraine as they continue to fight against Russian aggression," Ryder continued.

White House spokeswoman Karine Jean-Pierre said that the delivery of weapons from North Korea had contributed to Russia being able to wage its brutal war in Ukraine.

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"We don't believe any country should give Mr. Putin a platform to promote the war of aggression that we're obviously currently seeing in Ukraine and Russia," Jean-Pierre said, adding that the war "is blatantly violating the UN Charter and working to undermine the international system."

North Korea, which is largely isolated internationally due to its nuclear weapons program, has been accused by Ukraine's Western allies of supplying weapons and ammunition to Russia.

The governments in Moscow and Pyongyang have repeatedly dismissed those claims.

Putin was received by North Korean leader Kim Jong Un in Pyongyang on Tuesday evening.

According to observers, the two-day visit will, among other things, focus on arms deliveries from Pyongyang, which Moscow intends to use in its war against Ukraine.