At least 60 people were killed in a bomb attack on a school in eastern Ukraine, President Volodymyr Zelensky said late Sunday.

Luhansk region governor Serhiy Haidai said 90 people had been sheltered in the building in Bilohorivka and 30 had been rescued. Haidai said a Russian plane had dropped the bomb on Saturday.

Much of the region has been under Russian-backed separatist control for the past eight years.

Bilohorivka is near the government-controlled town of Severodonetsk, where heavy fighting was reported in the suburbs on Saturday. A Ukrainian newspaper, Ukrayinska Pravda, says the village became a “hot spot” during fighting last week.

The blast knocked down the building which caught fire and it took firefighters three hours to put out the blaze, according to the governor, writing in the Telegram.

He said almost the entire village was sheltered in the school basement.

The final death toll will be known only when the rubble has been cleared, the governor said.

UN Secretary-General Antonio Guterres said he was “horrified” by the deadly attack, adding: “Civilians must always be spared in time of war.”