Slipping back and forth across the front lines, the guerrilla fighters are known in Ukraine as partisans, and in recent weeks they have taken an ever more prominent role in the war, rattling Russian forces by helping deliver humiliating blows in areas they occupy and thought to be safe.

Increasingly, Ukraine is taking the fight against Russian forces into Russian-controlled areas, whether by using elite military units, like the one credited on Tuesday with a huge explosion at a Russian ammunition depot in the occupied Crimean Peninsula, or by deploying an underground network of the partisan guerrillas.

Last week, Ukrainian officials said, the partisans had a hand in a successful strike on a Russian air base, also in Crimea, which Moscow annexed eight years ago. It destroyed eight fighter jets.

“The goal is to show the occupiers that they are not at home, that they should not settle in, that they should not sleep comfortably,” said one guerrilla fighter, who spoke on condition that, for security reasons, he only be identified by his code name, Svarog, after a pagan Slavic god of fire.