GAZA CITY, Gaza Strip —  A rocket fired by Palestinian militants fell short of its target in Israel on Friday, striking a house in northern Gaza and killing two schoolgirls.

The attack came as Israel sent mixed signals regarding its plans for Gaza. Israeli defense officials say politicians have approved a large-scale incursion into the territory. But at the same time, Israel appeared open to international pressure against an invasion, prying open its border with Gaza on Friday to allow deliveries of humanitarian aid.

None of Gaza's militant factions claimed responsibility for the deadly rocket attack on the house in Beit Lahiya. Gaza Health Ministry official Dr. Moiaya Hassanain identified the two victims as 5-year-old Hanin Abu Khoussa and her 12-year-old cousin, Sabah Abu Khoussa. Three other young people were wounded, Hassanain said.

• Click here for photos.

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 not be impervious to international pressure to resume the truce.

A total of 106 trucks carried medicine, fuel, cooking gas and other vital goods into Gaza, 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 in 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 of the territory's 1.4 million residents. But 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 current 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.

Also Friday, a poll published in the Maariv daily showed Livni's moderate Kadima Party neck and neck with its hawkish Likud rival ahead of Feb. 10 elections. Likud objects to the peace talks that Israeli negotiators, led by Livni, are conducting with the government of moderate Palestinian President Mahmoud Abbas, who has ruled only the West Bank since Hamas' Gaza takeover.

A Teleseker survey showed Kadima winning 30 of parliament's 120 seats, to Likud's 29 seats. The poll surveyed more than 800 people and had a margin of error of 2 seats.