UN Secretary-General Antonio Guterres is "appalled" at the reported attack on a school in the Ukrainian town of Bilohorivka, where many people were apparently seeking shelter from fighting, his spokesperson Stephane Dujarric said Sunday.

Dujarric said Guterres reiterates that civilians and civilian infrastructure must be spared under international law.

"This war must end, and peace must be established in line with the Charter of the United Nations and international law. The United Nations and its humanitarian partners in Ukraine will continue supporting those whose lives have been shattered by war," said the spokesperson. 

The governor of Ukraine's Luhansk Oblast, Serhiy Haidai, said on Sunday that 27 people were rescued from the rubble and 60 were "most likely dead" after Russian forces dropped an air bomb on the school in Bilohorivka on the previous day.

Around 90 people were seeking shelter in the school when it was hit on Saturday, he said.

The bodies of two people were found at the building, he said, adding that "there is almost no hope that anyone survived. The aerial bomb exploded in the middle (of the building)."

The rescue operation is still underway, the governor added.

There has been no response yet from the Russian side.

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(With input from agencies)