Ukrainian drones struck deep inside Russia in an overnight attack targeting an oil facility serving a military airfield in the city of Engels, nearly 400 miles from the border, Ukraine’s military said Wednesday.

The Ukrainian military says it struck a fuel storage depot deep inside Russia. The strike caused a huge blaze at the facility that supplies an important Russian air base.

Russian authorities have declared a state of emergency in the Volga River port city of Engels as a huge fire, caused by a “massive” Ukrainian drone attack, rages unchecked. The strike was on the strategically important fuel storage tank farm for Engels Air Base,