An Israeli airstrike early Saturday hit a school compound in the northern Gaza Strip where displaced Palestinians were sheltering, killing dozens of people, according to Gaza officials.

The Israeli military acknowledged the attack but said Hamas and another armed Palestinian group were using the facility for military operations and attacks on Israel.

The strike in Gaza City, the latest in a string of attacks on schools turned into shelters, drew strong condemnation from the European Union and the United Nations, with Josep Borrell, the top EU diplomat, saying: "There’s no justification for these massacres.”