With its army short of ammunition and troops to break the deadlock on the battlefield, Ukraine has increasingly taken the fight behind Russian lines, attacking warships, railways and airfields in an attempt to diminish Moscow’s military operations.

Most recently, that campaign has focused on oil infrastructure, hitting refineries deep in Russian territory and driving home the country’s vulnerability to such attacks.

On Tuesday and Wednesday, Ukrainian drones hit four Russian refineries, officials on both sides said, adding to a series of recent attacks that have set fire to depots, fuel tanks and other oil infrastructure across Russia. Since the beginning of the year, Ukraine has claimed responsibility for nearly a dozen such assaults, and local Russian authorities have reported five more.

Experts and Ukrainian officials say Ukraine hopes to disrupt the Russian military’s logistical routes and combat operations by targeting refineries, which supply gasoline, diesel and fuel for tanks, fighter jets and other critical military equipment.

Beyond that, they hope to chip away at the profits that Moscow makes from the exports of oil products and cause disruptions in Russia’s domestic oil market.

Mikhail Krutikhin, an independent Russian energy analyst living in exile in Oslo, said the strikes had prompted Moscow to introduce a six-month ban on gasoline exports, starting March 1, to try to ensure that domestic demand is met while repairs are made to damaged refineries.