Ukraine has engaged militarily for the first time with South Korean troops that were deployed to support Russia in its ongoing war with its neighbor, Ukrainian President Volodymyr Zelenskyy said Tuesday in a nightly address. 

Zelenskyy did not go into detail about the engagement but warned of what he says is Russia’s intention to escalate the war that has raged for nearly 1,000 days. 

A Kyiv official said Ukraine’s army fired artillery at North Korean soldiers in Russia’s Kursk border region.

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"Terror, unfortunately, can spread like a virus when it does not meet sufficient counteraction. Now our counteraction must be sufficient, strong enough. The first battles with North Korean soldiers have opened a new chapter of instability in the world," Zelenskyy said in his nightly video address as he thanked Ukraine’s allies around the world.

"Together with the world, we must do everything so that this Russian step to expand the war with real escalation fails. Both for Russia and South Korea."

South Korea's Defense Ministry said on Tuesday that more than 10,000 North Korean troops had arrived in Russia, with a "significant number" in the frontline areas, including the Kursk region, where Ukrainian forces staged an incursion in August.

Defence Minister Rustem Umerov told South Korean state television there had been a "small engagement" with the North Korean troops, per Reuters. The report, with excerpts from the interview, quoted Umerov as saying that the engagement was small and not yet systematic in terms of mobilizing soldiers.

Umerov reportedly said he expects that five North Korean units, each consisting of about 3,000 soldiers, will be deployed to the Kursk area. North Korean soldiers are mixed with Russian troops and are misidentified on their uniforms, Umerov was quoted as saying, according to the Associated Press.

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Russia is reported to have 1.3 million active-duty soldiers with another 2 million in reserves. Russia is now seeing its highest number of casualties than at any other time since the war began, with some 1,200 casualties reported a day, claimed U.S. Secretary of State Antony Blinken last week. Despite the high number of troop casualties, there still does not appear to be any end in sight to the war — validating early concerns that this would be a war of attrition. 

Zelenskyy has been sounding the alarm that the recent deployment of North Korean troops in Russia not only spells trouble for Ukraine, but also draws into question the stability and security of nations in Asia that are allied with the West.

"North Korea’s actions aren’t random," Zelenskyy said in a frank interview with South Korea’s public broadcasting network KBS on Thursday. "They have strategic goals."

"Their actions aren’t coincidental — they want Russia’s support in return," he added in comments also posted to his social media account on X.

Zelenskyy has called on South Korea to take a bigger role in the conflict and has said that South Korea has already pledged to send a team of specialists to Ukraine where they will collaborate on defensive capabilities, including air defense, as North Korea also provides Russian with artillery and missiles.

"If South Korea wants to understand the real capabilities of North Korea and its soldiers, it would benefit them to be here, to see and analyze the reality firsthand," he said. Consider how close North Korea is to Seoul [25-30 miles], the range of modern artillery, not even missiles." 

"Air defenses can’t counter artillery strikes. Our own towns were obliterated by artillery. I hope South Korea never faces this, but preparation is critical," Zelenskyy added.

Zelenskyy also called into question China’s "silence" with regard to the North’s recent involvement in the war. 

Meanwhile, North Korea was reported to have fired a barrage of short-range ballistic missiles into the sea on Tuesday.

The launch came days after North Korean leader Kim Jong-un supervised a flight test of the country's newest intercontinental ballistic missile designed to reach the U.S. mainland. In response to that launch, the United States flew a long-range B-1B bomber in a trilateral drill with South Korea and Japan on Sunday in a show of force.

The Associated Press and Reuters contributed to this report.