For the first time, Ukraine has engaged militarily with South Korean troops that were supposed to support Russia in the ongoing war with its neighbor, Ukrainian President Volodymyr Zelensky said in an evening speech on Tuesday.

Zelensky did not elaborate on the engagement but warned of Russia's intention to escalate the war, which has been going on for nearly 1,000 days.

A Kiev official said the Ukrainian army fired artillery at North Korean soldiers in the Russian border region of Kursk.

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Ukrainian President Volodymyr Zelensky and South Korean dictator Kim Jong Un. (Thierry Monasse/Getty Images, left, and “KCNA,” the acronym for Korean Central News Agency, right.)

“Unfortunately, terror can spread like a virus if it is not met with sufficient countermeasures. Now our counteraction must be sufficient and strong enough. The first battles with North Korean soldiers have opened a new chapter of instability in the world,” said Zelensky. In his evening video address, he thanked Ukraine's allies around the world.

“Together with the world, we must do everything to ensure that this Russian move to expand the war with real escalation fails. For both Russia and South Korea.”

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

According to Reuters, Defense Minister Rustem Umerov told South Korean state television that there had been a “small skirmish” with North Korean troops. In the report, which included excerpts from the interview, Umerov was quoted as saying that the involvement was small and not yet systematic in terms of mobilizing soldiers.

FILE: In this photo provided by the North Korean government, North Korean leader Kim Jong Un (left) supervises artillery fire drills in North Korea on March 7, 2024. (Korean Central News Agency/Korea News Service via AP)

Umerov reportedly said he expected five North Korean units, each with about 3,000 troops, to be stationed in the Kursk area. Umerov was quoted as saying that North Korean soldiers were mixed in with Russian troops and misidentified on their uniforms, according to the Associated Press.

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Russia reportedly has 1.3 million soldiers on active duty and another 2 million in reserve. Russia is now recording its highest number of casualties since the war began, with about 1,200 casualties reported per day, US Secretary of State Antony Blinken claimed last week. Despite the high number of troop losses, there still appears to be no end to the war in sight – confirming initial fears that it would be a war of attrition.

Zelensky has sounded the alarm that the recent deployment of North Korean troops to Russia not only spells trouble for Ukraine but also calls into question the stability and security of Western-allied nations in Asia.

“North Korea’s actions are not a coincidence,” Zelensky said in a candid interview with South Korean public broadcaster KBS on Thursday. “They have strategic goals.”

“Their actions are not a coincidence – they want Russia’s support in return,” he added in comments also posted on his social media account on X.

Ukrainian President Volodymyr Zelensky attends a joint press conference with Ursula von der Leyen, President of the European Commission, in Kiev, Ukraine, Friday, September 20, 2024. (Christoph Soeder, pool photo via AP)

Zelensky called on South Korea to take a larger role in the conflict, saying that South Korea had already agreed to send a team of specialists to Ukraine, where they would work together on defense capabilities, including air defense, that North Korea also provides to Russia Provide artillery and rockets.

“If South Korea wants to understand the real capabilities of North Korea and its soldiers, it would be beneficial for them to be here to see and analyze the reality firsthand,” he said. Consider how close North Korea is to Seoul (25-30 miles), how long the range of modern artillery is, not even missiles.”

“Air defense cannot counter artillery attacks. Our own cities were destroyed by artillery. I hope South Korea never experiences anything like this, but preparation is crucial,” Zelensky added.

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Soldiers march in a parade marking the 70th anniversary of North Korea's founding in Pyongyang, North Korea, September 9, 2018. (AP Photo/Ng Han Guan, File)

Zelensky also questioned China's “silence” regarding the North's recent involvement in the war.

Meanwhile, North Korea reportedly fired a barrage of short-range ballistic missiles into the sea on Tuesday.

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

The Associated Press and Reuters contributed to this report.