This file photo, taken on Dec. 20, 2019, shows North Koreans at an airport in Vladivostok, Russia. Yonhap

Thousands of North Korean laborers have been sent to work in Russia last year, South Korea's spy agency said Sunday, in apparent violation of U.N. Security Council resolutions against Pyongyang.

The North is believed to have dispatched thousands of laborers to various construction sites across Russia last year, according to the National Intelligence Service (NIS), amid workforce shortages in Russia due to its ongoing war with Ukraine.

Under U.N. Security Council resolutions in response to North Korea's weapons tests, the country is banned from sending its nationals to work overseas, and all North Korean workers were required to return to their home country by December 2019.

North Korea and Russia are suspected of using student visas for the dispatch of North Korean workers.

Last year, 13,221 North Koreans entered Russia, up about 12 times from the previous year, Radio Free Asia recently reported, citing data from Russia's federal statistics service.

Among those who entered Russia last year, 7,887 of them said their visit was for education purposes.

The move comes amid North Korea's continued support for Russia's war efforts against Ukraine.

The North is estimated to have dispatched some 11,000 troops to Russia's western front-line region of Kursk to fight Ukrainian forces, according to South Korean officials. (Yonhap)