A Palestinian killed an Israeli-US girl with a knife after infiltrating a Jewish settlement on the southern West Bank, the Israeli military and witnesses said.
Hallel Ariel, aged 13, was declared dead after repeated resuscitation efforts failed, a spokeswoman for Jerusalem's She'arei Zedek hospital, Shoham Rubio, said.
The US State Department confirmed the girl was also a US citizen.
An Israeli man, aged around 30, who was a member of a security team that patrols the settlement, was also seriously injured, with both stab and gunshot wounds sustained during an attempt to overpower the attacker, first aid officials said.
The attacker was a 19-year-old from a nearby West Bank village, according to the Palestinian Health Ministry.
The Israeli military closed off the village, Bani Naim, by placing sand roadblocks at access roads, and surrounded the house of the attacker's family, the official Palestinian Wafa news agency reported.
Israeli Prime Minister Benjamin Netanyahu's office said he ordered the army to cordon off the village, to revoke work permits for members of the stabber's clan and to begin "procedures" to demolish the assailant's family home.
"My daughter was just sleeping. A happy, calm girl. A terrorist came and murdered her in her bed," the victim's mother, Rina Ariel, told reporters outside the hospital.
The settlement's security officer, Eyal Gelman, said security personnel in a lookout post saw the Palestinian climb over the settlement's security fence and immediately sent a team, which heard noise in the house nearest to the fence and burst inside.
"Everything happened very, very quickly. We got there really in a few minutes," he said.
The Palestinian stabbed one of the security team members, but was shot dead by another. The girl's father was on the patrol team, which found the girl stabbed in her bed.
"We enter the house. The father is with us. And inside we see her sleeping with more than eight stabbing wounds that I counted," Gelman told Israel Radio.
"The horrifying murder of a young girl in her bed underscores the bloodlust and inhumanity of the incitement-driven terrorists that we are facing," said Netanyahu.
"We will continue to take strong and determined action against terrorism everywhere and at all times," he said in a statement.
"I expect the Palestinian leadership to clearly and unequivocally condemn this vicious murder and take immediate action to stop the incitement."
UN Middle East envoy Nickolay Mladenov condemned "the gruesome murder" of the girl, noting that it was just one example of the violence that continues to put the prospects for peace in jeopardy.
Israel and the Palestinian areas have suffered a wave of violence since October, including dozens of knife attacks launched by Palestinians protesting the ongoing occupation and perceived Israeli violations - denied by Israel - at a disputed Jerusalem holy site.
The violence had appeared to have calmed down for several weeks, until two Palestinians killed four Israelis in a central Tel Aviv shooting attack in early June.
A second bout of violence occurred later Thursday when a Palestinian man pulled a knife in the coastal city of Netanya, stabbing a man and a woman before he was shot to death.
More than 220 Palestinians - most of them knife attackers and other assailants - and 34 Israelis have been killed amid the violence.