(CNN)About 60 people are feared dead after a Russian aircraft dropped a bomb on a school in Luhansk, eastern Ukraine, where civilians were sheltering on Saturday afternoon, a Ukrainian official said.
Serhiy Hayday, head of the Luhansk regional military administration, said the school building was destroyed.
"The explosion happened inside the building. Rescuers (are) dismantling the debris as quickly as possible. The chances of finding (anyone still) alive are very small. There were 90 people inside the school building; 27 survived, 60 people most likely died," Hayday said.
Hayday said a Russian air strike hit the school in the village of Bilohorivka, which is some seven miles from the frontlines of the ongoing conflict in eastern Ukraine, at around 4:37 p.m. (9:37 a.m. ET) on Saturday, causing fires to break out that took almost four hours to extinguish.
Russian forces have struck fleeing or sheltering civilians on numerous occasions since Moscow invaded Ukraine.
Schools, nurseries and hospitals have all been targeted by Russia, according to the United Nations.
Russian forces "must face justice for a series of war crimes" committed in the region northwest of Kyiv, following an investigation it conducted in Ukraine, Amnesty International said Friday.
The investigation, based "on dozens of interviews and extensive review of material evidence," has documented "unlawful air strikes on Borodyanka, and extrajudicial executions in other towns and villages including Bucha, Andriivka, Zdvyzhivka and Vorzel."
Fighting in Luhansk has been raging for months, and particularly since Russia refocused its invasion on the eastern Donbas region.
Hayday said on Ukrainian television on Saturday, hours before the school bombing, that the situation was difficult.
"The biggest efforts made by the enemy are to break through in Popasna and the direction of Severodonetsk and Voievodivka. That's where they deployed the biggest amount of their troops and equipment.
"That's where the largest number of shellings and rockets, and air strikes are constant -- it's just a terrible situation. Our guys are holding on, we are waiting for help, for reinforcement," he said.
CNN's Martin Goillandeau and Radina Gigova contributed reporting.