WASHINGTON, Aug. 3 (Xinhua) -- The United States is "appalled" by the "disgraceful" shelling outside a United Nations school in Gaza that killed at least ten Palestinian civilians, the State Department said on Sunday.

"We once again stress that Israel must do more to meet its own standards and avoid civilian casualties," spokeswoman Jen Psaki said in a statement.

The suspicion that militants are operating nearby does not justify strikes that put at risk the lives of so many innocent civilians, Psaki said, emphasizing that UN facilitates, especially those sheltering civilians, "must be protected."

Like all UN facilities in Gaza, the coordinates of the school which shelters some 3,000 displaced persons have been repeatedly communicated to the Israeli Defense Forces, Psaki said.

The spokeswoman said that the United States calls for a "full and prompt" investigation of this incident as well as the recent shelling of other UN schools.

The United States continues to underscore that all parties must take all feasible precautions to prevent civilian casualties and protect the civilian population and comply with international humanitarian law, she added.

In another incident of targeting UN facilities for sheltering, Israeli artillery fire hit a UN school in northern city Jabaliya on Wednesday, killing at least 15 people.