Gaza City, Gaza - The United Nations has protested the Israeli military bombing of Asma Elementary school where 400 Palestinians had taken shelter and three of them were killed, and a second school where 44 were killed, despite U.N. officials telling Israeli military officials that it was a U.N. school filled with civilians.

About 400 people who had fled their homes in Beit Lahiy because of violence there were being sheltered in the U.N.-run Asma Elementary school.

Asma Elementary was clearly marked as a U.N. installation, the United Nations Relief and Works Agency said in a statement Tuesday.

"Well before the current fighting, UNRWA had given to the Israeli authorities the GPS (global positioning system) co-ordinates of all its installations in Gaza, including Asma Elementary School," UNRWA officials said in a news release.

"UNRWA is strongly protesting these killings to the Israeli authorities and is calling for an immediate and impartial investigation," the agency continued. "Where it is found that international humanitarian law has been violated, those responsible must be held to account."

Three men from the same family were killed Monday night from a direct hit by an Israeli bomb on the school that took place just as the three left the school toilet.

Another U.N. facility, the Ash-Shouka School in Rafah, in the southern Gaza Strip, was also bombed Monday night and 44 Palestinian civilians were killed there, according to reports.

Other bomb attacks Monday night struck homes belonging to Hamas leaders, or people affiliated with Hamas.