GAZA CITY, Gaza Strip - A crude rocket fired by Palestinian extremists fell short of its target in Israel yesterday, striking a house in the northern Gaza Strip and killing two schoolgirls.

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 Hamas-run territory once rainy conditions clear.

At the same time, Israel appeared receptive to international pressure against an invasion, opening the Gaza border yesterday to allow in deliveries of humanitarian aid.

None of Gaza's extremist factions claimed responsibility for the deadly attack on the house in Beit Lahiya. Gaza Health Ministry official Moiaya Hassanain said the two victims, 5 and 12, were cousins. Three other children were wounded, he said.

The girls were the first Palestinian civilians inadvertently killed by extremists since Hamas' June 19 truce with Israel began collapsing six weeks ago.

Israel's crossings with Gaza have been largely clamped tight since Hamas seized control of the coastal strip in June 2007, with only the barest essentials allowed in since the truce with Gaza gunmen began unraveling.

On Thursday, however, Israel's Defense Ministry said it agreed to open its cargo crossings into Gaza to avert a humanitarian crisis there. Defense Minister Ehud Barak said the decision followed consultations with defense officials and calls from the international community.

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 schoolyards 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 gave Thursday in an interview with the Arabic- language TV station al-Arabiya: that Hamas was to blame for the suffering in Gaza, home to 1.4 million Palestinians.

But there were no immediate signs of a backlash against the extremists after the girls' deaths.

The gunmen kept up their fire on Israeli border areas despite Israel's agreement to open its crossings yesterday. In all, 13 rockets and mortars were fired toward Israel by last evening, the military said. One home was struck, but no injuries were reported.