A satellite image provided by the National Intelligence Service shows a Russian naval vessel suspected of transporting North Korean troops from the northeastern port of Chongji in North Korea. Oct. 18. Yonhap

One of the three pictures that South Korea's intelligence agency disclosed as evidence of North Korea's troop deployment to Russia was captured by a satellite that the South has been operating, a government source said Sunday.

Two of the three photos were attributed to Airbus, a global satellite imagery provider, but the third was not attributed when the National Intelligence Service (NIS) presented them Friday while confirming the North's deployment of troops to Russia for its war in Ukraine.

Disclosing the satellite images, the NIS said that the North has decided to send around 12,000 troops to Russia to support its war against Ukraine and has already deployed 1,500 special forces troops to Vladivostok.

"The unattributed photo was taken by a satellite that we've been operating," the source said.

That picture appears to have been taken by a satellite equipped with synthetic aperture radar (SAR) that can collect data regardless of the weather by using remote sensing systems.

South Korea has been operating multiple SAR-equipped satellites, including a military reconnaissance satellite, though images taken by military satellites are usually not included in government press releases as they are classified as military secrets.

South Korea has been closely tracking North Korea's movements using satellites operated by the government and the military amid growing speculation about deepening military cooperation between Moscow and Pyongyang. (Yonhap)