Israel vowed a harsh response after two Palestinian attackers slashed and shot to death four rabbis who were praying in a Jerusalem synagogue early Tuesday -- an attack that horrified Israelis, drew international condemnation and threatened to further inflame Jewish-Muslim tensions that were already running high over a contested holy site.
Israeli media later reported that a police officer injured while responding to the assault had died.
At least seven Israelis were hospitalized in the wake of the attack, the deadliest in Jerusalem since 2008. The two attackers, shot and killed by police units that converged on the scene within minutes, were identified as Palestinian cousins from predominantly Arab East Jerusalem, which has been a tinderbox for attacks in recent months.
The attackers -- armed with cleavers and handguns and said to have been shouting "God is great!" -- burst into the synagogue in the ultra-Orthodox Jerusalem neighborhood of Har Nof during morning prayers, witnesses said. Many devoutly religious immigrants to Israel have settled in the area, and three of the four rabbis killed held American citizenship, the State Department said. The fourth was a Briton, according to Israeli officials.
The White House identified the slain Americans as Aryeh Kupinsky, Cary William Levine and Moshe Twersky. The statement did not provide hometowns.
President Obama condemned the attack and said "it is all the more important for Israeli and Palestinian leaders and ordinary citizens to work cooperatively together to lower tensions, reject violence and seek a path forward towards peace."
Witnesses described panic and pandemonium, with the dead and wounded crumpling to the floor, clutching bloodied sacred texts. Those who managed to make their way out of the house of prayer burst onto the street screaming for help.
For many Israelis, the specter of a calculated attack on Jews at prayer, in ritual garments, carried chilling overtones of historic persecution.
"Jewish worshipers lay dead in pools of blood, still wrapped in prayer shawls and phylacteries, with holy books strewn on the floor," Yehuda Meshi-Zahav, who heads Zaka, an emergency response group led by Orthodox Jews, told Israel Radio. "Such sights I have never seen -- they recall dark days."
U.S. Secretary of State John F. Kerry called Israeli Prime Minister Benjamin Netanyahu and expressed condolences for the attack. "This simply has no place in human behavior," Kerry told reporters in London.
Netanyahu, who called top security officials to an emergency meeting, declared that the "despicable murderers" -- he also called them "animals" -- would not go unpunished. Within hours of the attack, a massive police contingent raided the family homes of the two assailants, identified as Udai Abu Jamal and Ghassan Abu Jamal, and Netanyahu later said the homes would be demolished and "inciters" held to account.
The two attackers "have no previous security records and did not operate within the framework of any organization," Yoram Cohen, the head of domestic intelligence agency Shin Bet, told members of a parliamentary committee after the incident, the Haaretz newspaper reported.
A government statement said unspecified "additional decisions … have been made in order to strengthen security throughout the country." Israel had already redeployed hundreds of troops to the West Bank after a pair of lethal stabbing attacks last week.
After the latest attack, Israeli forces in East Jerusalem and several parts of the West Bank battled stone-throwing protesters, clashes that continued as night fell. A light-rail train passing through an Arab neighborhood of Jerusalem was pelted with rocks, forcing it out of service.
At Kerry's prompting, Palestinian Authority President Mahmoud Abbas issued a denunciation of the attack but he coupled it with a call for a halt to Israeli "intrusions" on a site in Jerusalem's walled Old City revered by both Jews and Muslims.
The militant Hamas movement, while not claiming any involvement, praised the attack. Celebratory gunfire rang out in the Hamas-dominated Gaza Strip and at several locations in the West Bank, and a group spokesman, Sam Abu Zuhri, called the attack a response to the "continuing crimes of the occupation."
The brutal nature of the assault, the shock of such a strike on a house of worship and the fact that it took place in a part of Jerusalem considered far removed from recent clashes boded ill for any calming of violence that has roiled Jerusalem for months.
Four people on the Israeli side have been killed in the last month in vehicular attacks by Palestinians, and, in a spreading of "lone wolf" attacks outside the city, a soldier last week was fatally stabbed in Tel Aviv, as was a Jewish woman outside a West Bank settlement bloc.
Much of the current burst of ill feeling is centered on the hilltop in the Old City that is revered by Jews as the Temple Mount and by Muslims as the Noble Sanctuary. Jews are allowed to visit the site but not pray there, and activists -- some from within Netanyahu's government -- have been calling for a change to that long-standing "status quo," infuriating Muslims across the Islamic world.
Kerry visited Jordan -- the formal custodian of the site -- last week to try to ease frictions, winning pledges from Netanyahu and Abbas in separate meetings for calming measures. But calls for moderation are likely to be lost in the outcry over the attack and any retaliatory strikes arising from it.
"We're at war," Israeli lawmaker Aryeh Deri, who comes from the neighborhood where the attack took place, told Israeli radio. Neighbors and relatives of the attackers described them as heroes of the Palestinian cause.
Palestinian media depicted the attack itself as retaliation, coming two days after an Arab bus driver was found hanged at a bus depot in the western part of Jerusalem. A forensic report ruled that there was no sign of foul play and that the death was a suicide, but Palestinian media reports sharply contested the impartiality of the examiners.
Tuesday's assault was the most lethal in Jerusalem in six years, since a yeshiva on the city's outskirts was attacked by a gunman, killing eight of the religious students. An off-duty army officer killed that attacker.
Sobelman is a special correspondent. Special correspondent Maher Abukhater in Ramallah, West Bank, contributed to this report.