Ukraine's intelligence service GRU says it has evidence of North Korean presence.
"The first units (from North Korea) have already arrived in the combat zone in the Russian-Ukrainian war," GRU reports.
Putin avoided confirming, but did not deny, the North Korean presence when he held a final press conference in connection with the Brics group meeting in Russian Kazan.
Russia has never doubted that the DPRK (official name of North Korea) is serious about cooperation with Russia, and we cooperate with our North Korean friends, Putin said according to the AFP news agency.
What we do is our business, he continued.
Significant escalation
The USA, South Korea, and NATO have all confirmed that North Korean soldiers have been deployed to Russia. Around 3,000 soldiers have or are about to arrive, according to information from intelligence services.
"If these forces are deployed to Ukraine, it means a significant escalation of North Korea's support for Russia's illegal war," said NATO's spokesperson Farah Dakhlallah in a written statement on Wednesday.
Ukraine's intelligence service has previously stated that 12,000 North Korean soldiers are in Russia.
The development in the Russian invasion war has already received strong international reactions.
A provocation
South Korea's President Yoon Suk-Yeol says that North Korean presence is a "provocation" that will not go unnoticed – and threatens global security. Yoon made the comments after a meeting with Polish President Andrzej Duda, who is visiting Seoul.
He said that the two leaders agree that North Korea's actions "threaten global security beyond the Korean Peninsula and Europe".
In parallel with Thursday's warning, members of the Russian lower house of parliament, the Duma, voted unanimously to approve a defense agreement between Russia and North Korea. It stipulates "mutual support" if either party is subjected to hostile action.
