Ukraine's SBU security service said on Tuesday it had detained a serviceman it accused of helping Moscow attack Ukrainian troops fighting in Russia's Kursk region by giving away their location. Ukrainian forces crossed the border into the Kursk region last August in a rapid offensive,

The serviceman, according to their investigation, was recruited by Russia via a Telegram channel where he posted pro-Russian comments. Tasked with infiltrating Ukraine’s military, the suspect first conscripted into a rear-area unit before transferring to a combat brigade operating on the Kursk front.

At the height of the campaign, Ukrainian forces controlled some 500 square miles of Russian territory. Now they hold just a small sliver of land along the border.