Israel has reopened crossings into the Gaza Strip to allow the delivery of humanitarian aid.
Israeli officials said Defence Minister Ehud Barak took the decision after talks with security chiefs and requests from the international community.
About 80 trucks with supplies such as medicine, food and other goods were expected to cross on Friday.
The move comes despite Israeli warnings to Palestinian militants in Gaza to stop their rocket attacks on Israel.
On Friday, 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.
Medical officials said the incident happened in the village of Beit Lahya. The Israeli military said its forces had not fired in that area of the Gaza Strip, AFP reports.
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 UN says the deliveries fall far short of what is needed.
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.
The ministry said a smaller number of rockets was fired on Friday morning than on previous days and therefore it was judged that the humanitarian need in Gaza was greater than the security need in Israel.
In November, Israel re-sealed the border with Gaza after temporarily opening it to allow in a limited amount of food and fuel. That step was taken after a rocket was fired at Israel from Gaza.
On Thursday, Israeli Prime Minister Ehud Olmert said he would not hesitate to strike Hamas and also Islamic Jihad militants in Gaza.
Separately, Israeli Foreign Minister Tzipi Livni said after Thursday's emergency talks in Cairo with top Egyptian officials that the latest escalation was "unbearable".
The BBC's Christian Fraser says some will see Ms Livni's visit as the first of several diplomatic steps Israel must take before launching military action.
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