About 80 trucks carrying medicine, food and other goods were expected to cross border on Dec. 26.

The move comes despite Israeli warnings to Palestinian militants in Gaza to stop their rocket attacks on Israel.

On Dec. 26, two Palestinian sisters - aged five and 12 - were killed when a mortar, apparently fired by Palestinian gunmen targeting Israel, hit their home in northern Gaza.

More than 50 rockets have been launched from Gaza in recent days, after the killing of three Hamas members by Israel. Friday's total of rockets and mortars was 13, Israel's military said.

A six-month ceasefire in Gaza between Israel and Hamas ended last week.

UN officials have warned that the Hamas-controlled territory is facing a humanitarian catastrophe. Four out of five Gazans are dependent on food aid and the UN warehouses there are now empty.

The Israeli Defence Ministry did not say for how long the Gaza crossings would remain open but a spokesperson said the security situation was re-evaluated on a daily basis.