President Vladimir Putin said on Friday that it was Russia’s business whether or not it decided to use North Korean troops and said that if Ukraine wanted to join NATO then Moscow could do what it wanted to ensure its own security.

The United States said on Wednesday that it had seen evidence that North Korea has sent 3,000 troops to Russia for possible deployment in Ukraine, a move that the West is casting as a significant escalation of the Ukraine war.

Ukraine’s military intelligence service said that the first North Korean units trained in Russia had been deployed in the Kursk region, a Russian border area where Ukrainian forces took a chunk of Russian land in August.