National Intelligence Service (NIS) Director Cho Tae-yong attends a parliamentary audit session at the spy agency's headquarters in Seoul, Tuesday. Joint Press Corps

Some of the North Korean troops deployed to Russia seem to have been moving to the front lines with Ukraine, South Korea's spy agency said, Tuesday, fueling speculation that North Korean troops' direct involvement in the Russia-Ukraine war is imminent.

In return for the military support, Pyongyang is receiving technological support from Moscow for its satellite project as well as enhancing economic cooperation with Moscow, the National Intelligence Service (NIS) said.

The NIS shared the information with lawmakers during a closed-door parliamentary audit into the agency, according to Rep. Lee Seong-kweun of the ruling People Power Party and Rep. Park Sun-won of the main opposition Democratic Party of Korea, who are leaders of the National Assembly's Intelligence Committee.

"North Korea's troop deployment in Russia is underway," the NIS was quoted as saying by the lawmakers. "We are confirming the possibility that some of the troops, including high-ranking military officers, have been moving to the front lines."

It estimated that at least 3,000 North Korean troops, many of whom are in their late teens and early 20s, are in Russia's front-line region of Kursk, but it is working with Ukraine to determine the exact numbers.

The agency also forecast that the North is likely to deploy around 10,900 soldiers in total by December.

According to the NIS, the Russian military is teaching over 100 military terms in Russian to North Korean soldiers, but the language barrier between Russian-speaking and Korean-speaking soldiers poses a challenge.

The NIS said it believes a Russian aircraft traveling between Moscow and Pyongyang on Oct. 23 and 24 carried key Russian security officials involved in North Korea's troop deployment.

It added that North Korean Foreign Minister Choe Son-hui's visit to Russia is likely seen as a move to coordinate responses to the troop deployment. The North's mouthpiece Korean Central News Agency reported, Tuesday, that a delegation led by Choe left for Russia on Monday.

"It's difficult to speculate since North Korea has not disclosed the purpose of her visit, but Choe's agenda may include coordinating specific responses to North Korea's troop dispatch to Russia," a senior unification ministry official said. The official noted that this marks her third trip in less than a year following January, when she met with Russian President Vladimir Putin, and September when she attended the Fourth Eurasian Women's Forum and the First BRICS Women's Forum.

Regarding potential provocations by the North, the NIS predicted Pyongyang may test intercontinental ballistic missiles (ICBMs) or even nuclear weapons after the U.S. presidential election next month.

The agency said North Korea is receiving technological and economic aid from Russia in return for the military cooperation. "We suspect North Korea is preparing to launch a surveillance satellite, which failed in May, through purchase of high-tech parts and technological support from Russia," it said.

It also assessed that the number of North Korean workers sent to Russia has been increasing steadily. "It is estimated that about 4,000 North Korean workers have been dispatched to Russia this year. Their monthly wage is estimated to be around $800," it said.

The spy agency said it has detected "internal unrest" among North Korean residents and soldiers following the deployment, prompting the reclusive regime to tighten control over its people.

"We have learned that military officers are prohibited from using cellphones and soldiers lie about their deployment to their families" the NIS said. "North Korea has been beefing up security for its leader Kim Jong-un due to fears of a possible assassination attempt."

North Korean Foreign Minister Choe Son-hui, center, shakes hands with Russian Ambassador to North Korea Alexander Matsegora before leaving for Moscow, Monday, in this photo provided by the North's mouthpiece Korean Central News Agency. Yonhap

The NIS' information was similar to intelligence from Ukraine and the U.S. On Monday, Ukrainian President Volodymyr Zelenskyy said he expects 12,000 North Korean soldiers in Russia "soon."

"Some 3,000 North Korean soldiers and officers are already on Russian territory, and they (Russia) will use both on our territory. We think they will soon have 12,000 on Russian territory," Zelenskyy said at a press conference while attending the 2024 Nordic Council meeting in Iceland.

President Yoon Suk Yeol held phone talks with Zelenskyy, Tuesday, and agreed to share information on the North's troop deployments and discuss countermeasures together.

During the call, Yoon strongly condemned Russia's "illegal" military cooperation with North Korea, including arms transfers and troop deployments, and agreed to respond jointly to the evolving situation.

"We will not sit idly by and watch North Korea's military collusion that threatens our security. We will track the situation closely and take all necessary measures step by step," Yoon said.

Zelenskyy thanked South Korea for its consistent support of Ukraine's sovereignty and territorial integrity and said it will dispatch a special envoy to Seoul soon.

"We discussed the involvement of North Korean military forces in Russia's invasion of Ukraine. The conclusion is clear: this war is becoming internationalized, extending beyond two countries," Zelenskyy wrote on X (formerly Twitter).

The U.S. warned that it will not impose new limits on Ukraine's use of American weapons if North Korea joins Russia's war.

"A portion of those soldiers have already moved closer to Ukraine, and we are increasingly concerned that Russia intends to use these soldiers in combat or to support combat operations against Ukrainian forces in Russia's Kursk region near the border with Ukraine," Pentagon spokesperson Sabrina Singh said.