The two 15-year-old pupils at Jabaliya's school were both shot in the head by Israeli soldiers inside their homes just a few blocks and several hours apart. Islam died almost immediately after the bullet smashed through her forehead as she baked bread with her mother in their yard on Sunday. Tahreer is still on life support at a Gaza hospital after an operation to remove shards of shattered skull from her brain.

She lies motionless, with little to suggest she is alive other than gentle breathing. Doctors do not expect her to survive.

Tahreer's mother, Intisar, was at her bedside yesterday.

"Oh Tahreer, my heart. I wish I were lying in this bed, not you," she whispered to her child. "She was sweeping the floor in front of the door," said Mrs Abu El Jidyan. "I was standing talking to her. We knew the Israeli soldiers were around, we knew they had snipers in the buildings on our street but we didn't expect what happened. They just shot her in the head. Her brains spilled out. She said: 'Mum, I'm hit'. She praised God and she collapsed."

There were two bullets. The first struck Tahreer in the head. As she fell, the second hit the wall behind her. "I've no doubt a sniper shot her deliberately. There was no fighting in the area. There were no other shots, only the ones that hit Tahreer," said her mother.

With her stood Tahreer's 14-year-old brother, Naser, who was wounded by shrapnel last week. Israeli forces killed their father 11 years ago during the first intifada.

Mrs Abu El Jidyan regrets preventing Tahreer from walking to school on Sunday morning. She thought it would be too dangerous to venture out of their home in Jabaliya's Sikka neighborhood because it is on the edge of the area occupied by Israeli troops and tanks last week. Snipers are posted in buildings overlooking their street and a tank is less than a block away.

"I wouldn't let her out of the house but it was dangerous at home too. When there was fighting, bullets came through the walls. We stopped using some rooms on the side where the Israelis are," she said.

Israeli and Palestinian human rights groups say that about half of the nearly 80 people killed by the army over the past week of "Operation Days of Penitence" are civilians. The military says it has carefully targeted Hamas and Islamic Jihad fighters with missile strikes.

But while the numbers are in dispute - in part because it is often hard to say whether youths in their mid to late teens are bystanders or part of the Palestinian resistance - there is no doubt that a growing number of children have been felled by Israeli snipers.

At Islam and Tahreer's school in Jabaliya yesterday morning, the headmistress, Rukaya Kamal al Budani, fielded calls from parents wanting to know if it was safe to send their girls. "If they can get here, it's safe," was her stock reply. But of 1,150 pupils, fewer than 200 turned up.

Before word reached the school about Tahreer, Mrs al Budani was getting to grips with the death of Islam.

She said. "I don't know how to deal with the girls. It's going to have a big impact on her classmates and friends. I'm shocked that no one in the free world condemns the killing of a child."

Then one of the male teachers tells Mrs al Budani about the shooting of Tahreer the previous day. The headmistress sits in silence.

Until June, the two young women had been classmates, but then Tahreer failed her exams and was held back for a year. Asmaa Abu Samaan walked to school with her each morning.

"I met her in front of my house each morning to walk to school. I did my homework with her. I keep thinking that if she is brain-dead and not killed perhaps she is still suffering. I can't stand it," she said.

Asmaa walked to school yesterday morning without her friend.” I walked against the wall hoping the soldiers can't see me. I want to go to school because I know the Jews do not want us to study because we need to be educated to build our country," she said.

But the killing went on as the conflict claimed the life of another teenage girl in the Gaza strip yesterday. Palestinian medics said Israeli soldiers fired about 20 bullets into 13- year-old Iman al-Hams, including five into her head.