Seoul, South Korea — South Korean intelligence has found that North Korea has dispatched 12,000 troops, including special operation forces, to support Russia’s war against Ukraine, news reports said Friday, a development that could bring a third country into the war and intensify a standoff between North Korea and the West.

The Yonhap news agency cited the National Intelligence Service as saying that they have already left the country and formed into four brigades. Other South Korean media outlets carried similar reports.

If confirmed, it would be North Korea’s first major participation in a foreign war. North Korea has 1.2 million troops, one of the largest militaries in the world, but it lacks actual combat experience.

North Korean troops deployed to Russia have been stationed in military bases across the country’s Far East and will likely be “deployed to front lines” in Ukraine after they’re trained, the NIS said Friday, according to Agence France-Presse.

Many experts question how much the North Korean troop dispatch would help Russia, citing North Korea’s outdated equipment and shortage of battlefield experience.

Experts also said North Korea likely received Russian promises to provide security support for Pyongyang in its intense confrontations with the U.S. and South Korea over its advancing nuclear program.

During a meeting in Pyongyang in June, North Korean leader Kim Jong Un and Russian President Vladimir Putin signed a pact stipulating mutual military assistance if either country is attacked, in what was considered the two countries’ biggest defense deal since the end of the Cold War.

The NIS didn’t immediately confirm the report, but South Korea’s presidential office said in a statement that President Yoon Suk Yeol had presided over an emergency meeting earlier Friday to discuss North Korea’s troop dispatch to Ukraine. The statement said participants of the meeting agreed that North Korea’s troop dispatch poses a grave security threat to South Korea and the international community.

But the presidential office gave no further details such as when and how many North Korean soldiers have been sent to Ukraine and what roles they are expected to play.

Russia has denied using North Korean troops in the war, with Kremlin spokesperson Dmitry Peskov describing the claims as “another piece of fake news” during a news conference last week, according to Russia media.

Ukrainian media reported earlier this month that six North Koreans were among those killed after a Ukrainian missile strike in the partially occupied eastern Donetsk region on Oct. 3.

On Thursday, Ukrainian President Volodymyr Zelenskyy said his government has intelligence that 10,000 troops from North Korea are being prepared to join Russian forces fighting against his country, warning that a third nation wading into the hostilities could turn the conflict into a “world war.”

“From our intelligence we’ve got information that North Korea sent tactical personnel and officers to Ukraine,” Zelenskyy told reporters at NATO headquarters. “They are preparing on their land 10,000 soldiers, but they didn’t move them already to Ukraine or to Russia.”

NATO Secretary-General Mark Rutte said the western alliance “have no evidence that North Korean soldiers are involved in the fight. But we do know that North Korea is supporting Russia in many ways, weapons supplies, technological supplies, innovation, to support them in the war effort. And that is highly worrying.”

The U.S., South Korea and their partners have accused Pyongyang of supplying Moscow with artillery shells, missiles and other equipment to help fuel its war on Ukraine

Outside officials and experts say North Korea in exchange possibly received badly needed food and economic aid and technology assistance aimed at upgrading Kim’s nuclear-armed military. Both Moscow and Pyongyang have repeatedly denied the existence of an arms deal between the countries.