Israel said it had scaled up a ground offensive in northern Gaza as part of an operation to extend so-called "security zones" that provide a protective buffer along the border with Israel.

The order came not long after Palestinian health authorities said dozens of people, including children, were killed in strikes on a school turned shelter. Israel said it was looking into the reports.

Israeli strikes have killed more than a dozen people in the Gaza Strip as Israel sent more ground troops into the Palestinian territory to ramp up its offensive against Hamas.