This handout from South Korea's National Intelligence Service (NIS) shows a satellite image taken of a military facility in Khabarovsk, Russia, Oct. 18. The NIS estimates that around 240 North Korean personnel were gathered in the area. Yonhap

North Korea has remained silent on its deployment of troops to Russia to aid its prolonged war against Ukraine, in the latest sign of growing military cooperation between Pyongyang and Moscow.

On Friday, South Korea's spy agency announced that North Korea had decided to send around 12,000 special forces to support Russia, with approximately 1,500 of them already deployed to Russia's Far East.

This marks the first time North Korea has deployed ground troops on such a large scale, although it has previously dispatched small numbers of soldiers abroad to earn foreign currency.

North Korea has not released any official statement on its troop deployment to Russia.

The last time North Korea reported on the Ukraine war was Oct. 12, when the Rodong Sinmun, the North's main newspaper, published an article quoting a Russian military commander who claimed that Ukraine had used chemical weapons.

Russia has also not issued any formal reaction since South Korea's National Intelligence Service made public North Korea's troop deployment.

Observers say it would be difficult for North Korea to deny the dispatch due to evidence and may also be hesitant to publicize the deployment as sending soldiers into an active war zone would likely cause anxiety among its citizens.

"It is unlikely that North Korea will confirm this before Russia does," said Hong Min, a senior research fellow at the Korea Institute for National Unification.

Hong said since neither the United States nor the North Atlantic Treaty Organization has confirmed the deployment, it remains to be seen whether North Korean forces will actually engage in combat in the Ukraine war.

Regarding the situation, the South Korean government said it is closely monitoring developments.

"We are keeping all possibilities open and are carefully observing the situation," said Koo Byoung-sam, a spokesperson for the unification ministry, during a press briefing.

The defense ministry denounced North Korea over the latest development and vowed to take necessary measures to guard the safety of South Koreans.

"North Korea taking part in Russia's war of invasion is an illegal act that violates the U.N. Security Council resolutions and one that should be criticized by the international community," Jeon Ha-kyou, the spokesperson for the ministry, told a regular press briefing.

"We sternly denounce North Korea's behavior and strongly warn (the North) to immediately halt it," Jeon said, vowing to seek "necessary measures."

When asked if such measures could include South Korea's possible provision of lethal weapons to Ukraine, the official said the ministry will review measures with an open attitude.

Later Monday, Defense Minister Kim Yong-hyun expressed "serious concern" over deepening military cooperation between Moscow and Pyongyang, including the North's dispatch of troops to Russia, during his talks with U.S. Ambassador to South Korea Philip Goldberg.

South Korea's military, meanwhile, included foreign media reports on North Korea's troop deployment as it aired daily anti-North Korean propaganda broadcasts via loudspeakers along the border.

Monday's broadcast also included a Ukrainian media report on six North Korean soldiers who were killed during a recent missile attack.

The South's military has been conducting the broadcasts, believed to be audible to North Korean soldiers and residents in the border region, since July in response to the North's trash balloon campaign. (Yonhap)