The attack came as Israel sent mixed signals over its plans to respond to continuing Palestinian rocket fire. Israeli defense officials say politicians have approved a large-scale incursion into the territory once rainy conditions clear. But at the same time, Israel appeared receptive to international pressure against an invasion, opening the Gaza border Friday to allow in deliveries of humanitarian aid.
None of Gaza's militant factions claimed responsibility for the deadly attack on the house in Beit Lahiya. Gaza Health Ministry official Dr. Moiaya Hassanain said the two victims, ages 5 and 12, were cousins. Three other children were wounded, he said.
The girls were the first Palestinian civilians inadvertently killed by militants since their truce with Israel began collapsing six weeks ago. Family members and medics said they were killed by rocket fire.
Israel's crossings with Gaza have been largely clamped tight since Islamic Hamas militants seized control of the coastal strip in June 2007, with only the barest essentials allowed in since a June 19 truce with Gaza gunmen began unraveling six weeks ago.
On Thursday, however, Israel's Defense Ministry said it agreed to open its cargo crossings into Gaza to avoid a humanitarian crisis there. Defense Minister Ehud Barak said the decision followed consultations with defense officials and calls from the international community, suggesting Israel might be open to international pressure to resume the truce.
A total of 106 trucks carried medicine, fuel, cooking gas and other vital goods into Gaza, including a small donation from Egypt, the military said.
Cabinet Minister Binyamin Ben-Eliezer said the humanitarian shipment was meant to be a message to the people of Gaza that they were not Israel's enemy.
"We are sending them a message that the Hamas leadership has turned them into a punching bag for everyone," he told Israel Radio. "It is a leadership that has turned school yards into rocket-launching pads. This a leadership that does not care that the blood of its people will run in the streets."
Ben-Eliezer echoed the message Prime Minister Ehud Olmert tried to deliver a day earlier in an interview with the Arabic language Al-Arabiya TV station: that Gaza's Islamic Hamas militant rulers were to blame for the suffering in Gaza, home to 1.4 million Palestinians.
But, as with similar cases involving unintended civilian casualties in the past, there were no immediate signs of backlash against the militants after the girls' death.
The militants kept up their fire on Israeli border areas despite Israel's agreement to open its crossings Friday. In all, 13 rockets and mortars were fired toward Israel by Friday evening, the military said. One home was struck but no injuries were reported.
Israel had originally agreed to open the cargo crossings with Gaza on Wednesday, but shut the passages after militants began pounding southern Israel with rockets and mortars.
Pressure has been mounting in Israel for the military to crush Gaza militants, and Israeli leaders have been voicing strong threats in recent days. But on Friday, military officials said the army was planning a routine rotation of its troops along the Gaza border in the coming week. That, coupled with winter weather, made an imminent operation seem unlikely, they said.
The officials spoke on condition of anonymity because they are not permitted to discuss military strategy publicly.
Israel left Gaza in 2005 after a 38-year occupation and has been reluctant to press ahead with a campaign likely to exact heavy casualties on both sides. Past incursions have not halted the barrages, and officials fear anything short of a reoccupation of Gaza would fail to achieve the desired results.