Two attackers armed with knives, axes and a gun stormed a synagogue in an Orthodox Jewish neighborhood early Tuesday, killing four worshipers and wounding several others before police shot them dead.

Israeli Prime Minister Benjamin Netanyahu responded quickly, convening his security cabinet and announcing that Israel will “respond harshly.” He called it a “cruel murder of Jews who came to pray and were killed by despicable murderers.”

The early morning attack was the worst attack in Jerusalem in years — harkening back to the worst days of the Palestinian intifadas, or uprisings, and is certain to enflame a city already on a knife-edge amid rising tensions between Jews and Palestinians over a contested religious site.

Netanyahu blamed the attack on incitement by the Islamic militant group Hamas, which runs the Gaza Strip, and Palestinian Authority President Mahmoud Abbas, leader of the West Bank Palestinians. He claimed the international community had turned a blind eye to the incitement by the Palestinian leadership.

Hamas, which fought a war against Israel this past summer in Gaza, praised the attack, but stopped short of claiming responsibility. Loudspeakers at mosques in Gaza called out congratulations, according to news reports from the Gaza Strip.

“What I saw was horrifying,” said Avi Nefoussi, a paramedic, who was among the first to enter the synagogue minutes after the two attackers were shot dead by police. “I saw several bodies lying on the floor, some were people that I knew, and two people badly injured from gun shots.”

Israeli police called the assault a terrorist attack and said the two assailants were apparently Palestinians from east Jerusalem, which has been the scene of almost daily clashes between police and Palestinian protesters in recent months.

Police spokesman Micky Rosenfeld said six people were also wounded in the attack, including two police officers. He said police were searching the area for other suspects. Police secured the area around the synagogue.

Palestinian media reported that the two attackers were Udai and Ghassan Abu Jamal, cousins from the east Jerusalem neighborhood of Jabl Mukabr. Israeli media said that one of the two men worked in a supermarket near the synagogue.

In London, Secretary of State John F. Kerry angrily condemned the attacks and demanded that the Palestinian leadership take immediate steps to end incitement to violence among Palestinians.

“Innocent people who had come to worship died in the sanctuary of a synagogue,” Kerry said shortly after the attack, his voice quavering. “They were hatcheted, hacked and murdered in that holy place in an act of pure terror and senseless brutality and murder,” he said after speaking by phone with Netanyahu.

“I call on Palestinians at every single level of leadership to condemn this in the most powerful terms. This violence has no place anywhere, particularly after the discussion that we just had the other day in Amman.”

Netanyahu, Kerry and Jordan’s King Abdullah II met last week in Jordan in a bid to ease tensions and restore calm after months of violent confrontations between the two sides over access to a sacred shrine holy to both Jews and Muslims.

Abbas also condemned the attack. “The presidency condemns the attack on Jewish worshippers in their place of prayer and condemns the killing of civilians no matter who is doing it,” his office said in a statement given to the Reuters news agency.

“What happened in the synagogue is a red line for the Israeli government and maybe this could change all events,” said Shaul Bartal, a retired Israeli major who served in various military positions in the West Bank.

He said that many Arab residents of East Jerusalem currently work in Jewish neighborhoods in the city. However, in light of this attack and others over the past few weeks, Israel might be forced to make changes in their status.

The site of the synagogue, Har Nof, is a quiet Orthodox neighborhood on the western side of Jerusalem, away from Arab neighborhoods in East Jerusalem. Palestinians refer to it as Dier Yassin, however, a former Palestinian village from before the 1948 creation of the state of Israel.

A spokesman for Hamas said on Twitter that the attack was a natural reaction to Israel’s treatment of Palestinians.

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