Six North Korean soldiers were reportedly killed on the Russian front line near the Donetsk region in eastern Ukraine.

Citing intelligence sources Friday, Ukrainian media outlet the Kyiv Post said out of more than 20 military personnel killed in a Ukrainian missile strike the previous day, six were North Korean officers. 

At least three other North Korean soldiers were injured.

The Russian Telegram channel Kremlin Snuffbox, citing an unnamed military source, said Russian soldiers were showing the North Korean officers how Moscow was preparing for assault operations and countering U.S. weapons at the time of the attack.

Last year, Ukraine's Main Intelligence Directorate disclosed that personnel from the North Korean military, including engineer units, were working in the Russian-occupied territory near Donetsk.

Amid increasing military cooperation between the North and Russia since the outbreak of the war in Ukraine, Kyiv also reported last year that Moscow had persuaded Pyongyang to send its citizens to the territories of Donetsk and Luhansk to carry out construction work.