Although the circumstances of Norhan Deeb's death were unclear, the violence strained the recent atmosphere of goodwill between Israeli Prime Minister Ariel Sharon and the new Palestinian leader, Mahmoud Abbas.
Despite the heightened tensions, top Israeli and Palestinian security officials met later Monday to work out the details of a handover of several West Bank towns to Palestinian control. No agreements were announced.
Deeb was killed in the courtyard of a U.N. school in the Rafah refugee camp. The camp, located near the Egyptian border, is a frequent flashpoint of violence between Israeli troops and Palestinian gunmen.
Palestinian witnesses said the gunfire came from a nearby Israeli military position along the border.
The Israeli military said it checked the claims and found two cases in which soldiers opened fire, but neither was in the area where the girl was shot. "According to our examination, the girl apparently was not shot by Israeli army gunfire," the military spokesman's office said.
A military official, speaking on condition of anonymity, said Palestinian revelers had been shooting into the air in the area, celebrating their return from the Hajj pilgrimage to Mecca.
Residents, however, said there were no such celebrations, and Dr. Ali Moussa, the physician who treated the girl, said she was hit by a bullet directly in the face. But he said initial reports by paramedics that she had been killed by tank fire were wrong.
Witnesses said the girl was shot in the head as she and other pupils lined up in the schoolyard for afternoon assembly.
"I didn't hear any shooting. Suddenly, I heard Norhan screaming. Then she fell down," said Aysha Khateeb, a classmate who was wounded in the hand. "I looked at my hand and saw blood."
Khateeb spoke to The Associated Press from her hospital bed, and burst into tears as the covered body of her classmate was wheeled by on a stretcher.
Johan Eriksson, a spokesman for the U.N. Relief and Works Agency, said U.N. officials weren't able to definitively identify the source of the gunfire, but that all signs pointed to the Israeli troops.
"The only firing that took place at that time in the entire Rafah area" came from the direction of an Israeli observation post, he said.
Residents who live near the observation post said they heard firing from that area. However, none of the witnesses actually saw any shots being fired.
Hours later, Palestinian militants fired at least six rounds of mortar shells at Jewish settlements in Gaza, damaging one house in the Neve Dekalim settlement, the Israeli army said. The Islamic group Hamas claimed responsibility, saying it was avenging the girl's death.
Later Monday, Hamas and seven other militant factions issued a statement threatening to retaliate against Israel "if the crimes continue," implying that it would hold its fire if there is no further violence.
The violence upset a recent lull.
Abbas has won a commitment from militant groups to stop attacks and deployed thousands of officers throughout Gaza over the past 10 days to ensure the quiet. Although no formal cease-fire has been declared, Israel has scaled back military operations in return.
In the Israeli-Palestinian security meeting that began after nightfall Monday, Israeli Defense Minister Shaul Mofaz and Palestinian negotiator Mohammed Dahlan were to complete preparations for a security handover in the West Bank, but the renewed violence dominated the talks.
Israeli defense officials said Mofaz told Dahlan that the Palestinian Authority must stop the firing of mortars, regardless of the explanation that it was retaliation for the killing of the girl. The officials, speaking on condition of anonymity, said Palestinian police must move forward from deployment to action to stop attacks. He said their performance in Gaza would influence the extent to which Israel would hand over responsibility in the West Bank, the officials said.
The officials said Israel would reopen the Rafah crossing between Gaza and Egypt on Tuesday. The crossing has been closed since Dec. 12, when Palestinians tunneled under the Israeli military base there and blew it up, killing five soldiers.
Palestinian Cabinet secretary Hassan Abu Libdeh, who took part in the talks, said no agreements were reached, and another meeting would take place in the coming days.