CNN: As civilian casualties mount in Gaza in the ongoing Israel-Hamas conflict, the United Nations' top human rights official warned of possible war crimes having been committed. U.N. High Commissioner for Human Rights Navi Pillay called for "real accountability considering the increasing evidence of war crimes and an ever-growing number of civilian casualties, including some 250 children."

She cited six United Nations schools in Gaza have been struck, resulting in the deaths of civilians. The United Nations has blamed Israel for the strikes, but Israel says its military only responded to fire and did not target the schools.

"The shelling and bombing of UN schools which have resulted in the killing and maiming of frightened women and children and civilian men, including UN staff, seeking shelter from the conflict are horrific acts and may possibly amount to war crimes," Pillay said in a statement.

Pillay didn't excuse the Hamas militants, either. She once again condemned the indiscriminate firing of rockets into Israel, and the placement of military assets close to densely populated areas. But the biggest concern appeared to be the shelling of the schools.

"If civilians cannot take refuge in UN schools, where can they be safe?" Pillay asked. "They leave their homes to seek safety -- and are then subjected to attack in the places they flee to. This is a grotesque situation."

Another top U.N. official, Undersecretary for Humanitarian Affairs Valerie Amos, said there is a need for Israel and Hamas to comply with humanitarian and human rights law.