KYIV, Ukraine (AP) — North Korean troops are ready to be deployed by Russia to the battlefield in Ukraine as early as this weekend, Ukrainian President Volodymyr Zelensky claimed Friday.

Western officials have warned that North Korean units joining the fight would inflame the situation almost three years of war and bring geopolitical consequences into the Indo-Pacific region.

The possibility has alarmed world leaders and heightened diplomatic tensions.

White House national security spokesman John Kirby said Friday that the top national security advisers of the United States, Japan and South Korea had met and expressed “grave concern” about North Korea's troop build-ups for possible use with Russia on the battlefield against Ukraine would have expressed.

Kirby said the three countries' national security advisers “urge Russia and the Democratic People's Republic of Korea to end these actions, which only serve to extend the security implications of Russia's brutal and illegal war beyond Europe and into the Indo-Pacific.”

“It is possible that more than 3,000 troops from North Korea have now been sent to Russia for equipment and training,” Kirby said in a phone call with reporters.

Kirby said the U.S. government had no firm intelligence estimates about where the troops would go, “but we believe it is certainly possible” and “perhaps even likely” that some of North Korea's troops would be stationed in Russia's Kursk region Ukraine has held some territory since its conquest in August. However, he warned that he did not know in what capacity and for what purpose the North Korean troops would be used.

A senior official in the Ukrainian presidential office told The Associated Press on Friday that Zelensky had canceled a planned visit to Kiev by U.N. Secretary-General Antonio Guterres.

The official, who spoke on condition of anonymity because he was not authorized to speak publicly about the matter, said the visit should have taken place later this week's summit in the Russian city of Kazan of the BRICS bloc of developing countries, in which Guterres took part.

A photo of Guterres shaking hands with Russian President Vladimir Putin at the summit sparked an outcry in Ukraine.

Zelensky said in a post on Telegram that Ukrainian intelligence had determined that between Sunday and Monday “the first North Korean military will be deployed by Russia in combat zones.”

He said on Telegram that the deployment was “an obvious escalatory step by Russia.” He did not give any further details, including where the North Korean soldiers could be sent.

Russia is waging a bitter campaign along Ukraine's eastern front this summer, gradually forcing Kiev to give up the ground. But Russia has struggled to expel Ukrainian forces from the Kursk border region that follows it an idea almost three months ago.

North Korean units were discovered in Kursk on Wednesday, Ukraine's Main Intelligence Directorate, known by the acronym GUR, said.

The soldiers completed several weeks of training at bases in eastern Russia and were equipped with clothing for the upcoming winter, GUR said in a statement late on Thursday.

She estimated the number of North Korean soldiers sent from Pyongyang to Russia at around 12,000, including around 500 officers and three generals.

GUR provided no evidence to support its claims.

Dutch Defense Minister Ruben Brekelmans said on the social platform

The deployment of North Korean forces as part of a military pact between Moscow and Pyongyang gives the conflict a new dimension. It is Europe's largest war since World War II and has cost tens of thousands of lives on both sides, including many civilians.

The USA announced this on Wednesday 3,000 North Korean soldiers are deployed to Russia and train at multiple locations, making the move very serious.

Zelensky said a week ago that his government had intelligence information about it 10,000 soldiers from North Korea are being prepared to join the Russian forces fighting against his country. He said a third country joining the hostilities would turn the conflict into a “world war.”

North Korea had already supplied Russia with ammunition as part of a defense pactbut ground troops could significantly complicate a war that has inflamed international politics and most Western countries are supporting Kiev.

Putin, on the other hand, does sought support from the BRICS countries.

He neither confirmed nor denied the presence of North Korean troops in Russia.

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Mike Corder in The Hague and Josh Boak in Washington contributed.

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Follow AP's coverage of the war in Ukraine at https://apnews.com/hub/russia-ukraine