South Korea's spy agency said Friday that North Korea has dispatched troops to support Russia's war against Ukraine. If confirmed, the move would bring a third country into the war and intensify a standoff between North Korea and the West.

The South Korean announcement came a day after 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.

US 'CONCERNED' ABOUT REPORTS OF NORTH KOREAN SOLDIERS FIGHTING ALONGSIDE RUSSIA IN UKRAINE

The National Intelligence Service said in a statement that Russian navy ships transferred 1,500 North Korean special operation forces to the Russian port city of Vladivostok from Oct. 8 to Oct. 13. It said more North Korean troops are expected to be sent to Russia soon.

The North Korean soldiers deployed in Russia have been given Russian military uniforms, weapons and forged identification documents, the NIS said. It said they are currently staying at military bases in Vladivostok and other Russian sites such as Ussuriysk, Khabarovsk and Blagoveshchensk, and that they will likely be deployed to battle grounds after completing their adaptation training.

The NIS posted on its website satellite and other photos showing what it calls Russian navy ship movements near a North Korean port and suspected North Korean mass gatherings in Ussuriysk and Khabarovsk in the past week.

South Korean media, citing the NIS, reported that North Korea has decided to dispatch a total of 12,000 troops formed into four brigades to Russia. The NIS said it could not confirm the reports.

The NIS has a mixed record in finding developments in North Korea, one of the world's most secretive countries. If confirmed, the move would be North Korea’s first major participation in a foreign war. North Korea has 1.2 million troops, one of the largest standing militaries in the world, but it hasn’t fought in large-scale conflicts following the 1950-53 Korean War.

Asked about the NIS finding, NATO Secretary-General Mark Rutte said "At this moment, our official position is that we cannot confirm reports that North Koreans are actively now as soldiers engaged in the war effort, but that may change."

Pentagon Press Secretary Maj. Gen. Pat Ryder told reporters Thursday that the U.S. couldn’t confirm or corroborate media reports on the North Korean troop dispatch to Russia.

Russia has earlier denied using North Korean troops in the war, with presidential spokesman Dmitry Peskov describing the claims as "another piece of fake news" during a news conference last week. North Korea's state media hasn't commented on the issue.

North Korea and Russia, locked in separate confrontations with the West, have sharply boosted their cooperation in the past two years. The U.S., South Korea and their partners have accused North Korea of supplying artillery shells, missiles and other conventional arms to Russia to help fuel its war on Ukraine in return for economic and military assistance. 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.

Many experts question how much the North Korean troop dispatch would help Russia, citing North Korea’s outdated equipment and shortages of battle experience. They say North Korea likely received Russian promises to provide it with high-tech weapons technology associated with its nuclear and missile programs, a move that will complicate U.S. and South Korean efforts to neutralize North Korea nuclear threats.

"Diplomatically, Pyongyang would be sacrificing its relations with European countries for the foreseeable future. The quid pro quo in terms of Russian military technology provided to the Kim regime could be significant enough to threaten South Korea’s security," said Leif-Eric Easley, professor of international studies at Ewha Womans University in Seoul.

Hong Min, an analyst at Seoul’s Korea Institute for National Unification, believed Russia has likely offered technology transfers related to intercontinental ballistic missiles, nuclear-powered submarines and surface-to-air defense systems that would enhance North Korea's deterrence posture against the U.S. and South Korean forces.

Hong said Kim may also see the troop dispatch as a crucial opportunity to expose his soldiers to modern weapons technology and warfare and test their combat capabilities.

Earlier Friday, South Korean President Yoon Suk Yeol convened an emergency security meeting to discuss the fallout of the North Korean troop dispatch. Meeting participants agreed that North Korea’s troop dispatch poses "a grave security threat" to South Korea and the international community, according to Yoon's office.

Tensions on the Korean Peninsula have intensified in recent years, with Kim sharply increasing the pace of provocative missile tests and openly threatening to use nuclear weapons preemptively. South Korea and the U.S. have responded by expanding their military exercises, which North Korea views as invasion rehearsals.

On Thursday, Zelenskyy warned 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."

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.

Many experts were earlier skeptical of possible North Korean troop deployments to Russian-Ukraine battlefields because North Korea is preoccupied with its nuclear standoff with the U.S. and South Korea.

North Korea sent pilots to fight for North Vietnam during the Vietnam war and for Egypt during the Yom Kippur War in 1973, but there have been no known large-scale dispatch of its ground troops overseas.

There have been speculations that North Korea has likely sent military technicians and engineers to support Russia's use of North Korean weapons and learn their wartime performances.

Easley, the professor, said "it would be surprising if Pyongyang deployed thousands of soldiers to fight as hired mercenaries." But he added North Korea could have sent construction workers, technicians, engineers, and military intelligence officers to Russian-controlled enclaves.