Bankir and his men have been trying to fight off Russian attacks along the Ukrainian front lines for more than two years. But it’s only now that they are finally able to strike where it hurts: Inside Russia’s own territory.

The newly granted permission by the United States and other allies to use Western weapons to strike inside Russia has had a huge impact, Bankir said. “We have destroyed targets inside Russia, which allowed for several successful counteroffensives. The Russian military can no longer feel impunity and security,” the senior officer in Ukraine’s Security Service (SBU) told CNN. For security reasons, he asked to be identified by his call sign only.