A huge explosion rocked a Russian ammunition depot on the occupied Crimean Peninsula on Tuesday morning, striking another embarrassing blow to Moscow’s forces a week after blasts at a Russian air base in the same region destroyed several fighter jets.

A senior Ukrainian official, speaking on the condition of anonymity to discuss the operation, said that an elite Ukrainian military unit operating behind enemy lines was responsible for the explosion, which sent up a huge fireball. Although Ukraine’s leaders did not publicly claim responsibility, an adviser to President Volodymyr Zelensky confirmed that the explosion had occurred.

The adviser, Mykhailo Podolyak, also appeared to hint at Ukrainian involvement. “A reminder: Crimea of normal country is about the Black Sea, mountains, recreation and tourism, but Crimea occupied by Russians is about warehouses explosions and high risk of death for invaders and thieves. Demilitarization in action,” he wrote on Twitter.