United Nations Secretary-General Antonio Guterres said on Monday that the protection of civilians "must be paramount" in the conflict between Israel and Palestinian militants Hamas, warning that the Gaza Strip was becoming "a graveyard for children."

"Ground operations by the Israel Defense Forces and continued bombardment are hitting civilians, hospitals, refugee camps, mosques, churches and U.N. facilities — including shelters. No one is safe," Guterres told reporters.

"At the same time, Hamas and other militants use civilians as human shields and continue to launch rockets indiscriminately towards Israel," he said.

He said clear violations of international humanitarian law were being committed and again appealed for a humanitarian ceasefire.