UN Secretary-General Antonio Guterres is "appalled" by the bombing of a school in eastern Ukraine that left 60 people dead and called for civilians to be spared, his spokesperson said Sunday.

"The Secretary-General is appalled by the reported attack on 7 May which hit a school in Bilohorivka, Ukraine, where many people were apparently seeking shelter from the ongoing fighting," spokesman Stephane Dujarric said in a statement.

Guterres "reiterates that civilians and civilian infrastructure must always be spared in times of war," and noted that the attack was "yet another reminder that in this war, as in so many other conflicts, it is civilians that pay the highest price."