The Russian military said Wednesday that it used long-range missiles to destroy a depot in Ukraine’s western Lviv region that housed ammunition for NATO-supplied weapons, and the governor of a key eastern city acknowledged that Russian forces are advancing amid heavy fighting.

Separatists backed by Russia accused Ukrainian forces of sabotaging an evacuation of civilians from the city’s besieged Azot chemical plant, where about 500 civilians and an unknown number of Ukrainian fighters are thought to be hiding from missile attacks. That claim could not be verified.

Russian officials announced a humanitarian corridor from the Azot plant the day before, saying it would take civilians to areas controlled by Russian forces rather than Ukrainian forces.

Many previously announced planned evacuations from other conflict zones in Ukraine have failed, with both sides blaming the other. Some Ukrainians have been hesitant to flee to Russian-controlled territory.

Serhiy Haidai, the Ukrainian governor of Luhansk, told The Associated Press that “heavy fighting in Sievierodonetsk continues today as well.” The situation in the city is deteriorating, according to Haidai, because Russian forces have more manpower and weapons.

“However, our military is holding back the enemy from three sides at the same time,” Haidai explained.

“The enemy is advancing due to a significant advantage in artillery and people, but the Ukrainian army is defending its city positions.”

According to Russian Defense Ministry spokesman Igor Konashenkov, Russian forces destroyed the depot near the town of Zolochiv in the Lviv region near the border with NATO member Poland using high-precision Kalibr missiles.

Konashenkov stated that shells for M777 howitzers, which were supplied by the US, were stored there. He claimed that four howitzers were destroyed in other battles, and that Russian airstrikes also destroyed Ukrainian “aviation equipment” at a military aerodrome in the southern Mykolaiv region.

The Ukrainians made no immediate comment on the Zolochiv strike.