World Bulletin/News Desk

The United States criticized the "disgraceful shelling" at a U.N. school in Gaza on Sunday and urged Israel to do more to prevent civilian casualties in its attacks.

State Department spokeswoman Jen Psaki also called for an investigation into attacks on U.N. schools in densely populated Gaza.

"The United States is appalled by today's disgraceful shelling outside an UNRWA school in Rafah sheltering some 3,000 displaced persons, in which at least ten more Palestinian civilians were tragically killed," Psaki said in a statement.

Psaki urged Israel again to live up to its "own standards of avoiding civilian casualties" as the conflict in  Gaza stretched into its 27th day.

On Wednesday, at least 15 Palestinians who sought refuge in a U.N.-run school in Jabalya refugee camp were killed during fighting, and the United Nations said Israeli artillery had apparently hit the building.

Psaki said U.N. facilities should not be used as bases from which to launch attacks.

"The suspicion that militants are operating nearby does not justify strikes that put at risk the lives of so many innocent civilians," she added.