In apparent retaliation for an Israeli military raid in the West Bank a day earlier, a Palestinian gunman killed seven worshippers outside a Jerusalem synagogue.
Three Israelis were also wounded in the Sabbath-eve massacre, which marked the deadliest attack against Israelis in over a decade.
One of the victims was a 70-year-old woman, and several others were in their 60s. Among the wounded was a 15-year-old boy.
The bloodshed sparked celebrations in the West Bank and Gaza Strip, where Palestinians fired bullets into the air, shouted “God is great!” and distributed sweets.
A series of Israeli airstrikes followed a barrage of rockets fired by Gaza into Israel, which led to the carnage in Neve Yaakov, a religious Jewish settlement in east Jerusalem.
In spite of this, there were no casualties reported from those attacks, which appeared to be deliberately limited to avoid provoking an all-out war.
In a statement to reporters, Benjamin Netanyahu said he held a security assessment and decided on “immediate actions,” with his Security Cabinet to discuss any further responses on Saturday night.
According to Netanyahu, Israel will act with “determination and composure”.
However, he declined to elaborate.
In addition, he urged the public not to seek vigilante justice.
An Israeli raid in Jenin killed nine people, including seven Palestinian militants and a 61-year-old woman.
During fighting in Jerusalem, a 10th Palestinian was fatally shot, marking the deadliest single raid in the West Bank in two decades.
Although there was no immediate claim of responsibility for the attack, a Hamas spokesman called it “a revenge and natural response” to Israeli raids in Jenin.
Police said the Jerusalem shooter fled in a car after opening fire and was killed after cops chased him down.
According to reports, he was a 21-year-old resident of east Jerusalem who appeared to be acting alone.
In response, Jerusalem Police Chief Doron Turjeman promised that an “aggressive and significant” investigation would be conducted to find any accomplices.
Among the dead were five men and two women, including several who were 60 or older, according to Israeli MADA rescue services.
The Hadassah Hospital in Jerusalem reported that a 15-year-old boy was recovering from surgery after he was wounded.
Antony Blinken, US Secretary of State, was scheduled to visit the region on Sunday when the attack occurred.
In a statement, White House Press Secretary Karine Jean-Pierre said that the US strongly condemned the shootings and was “shocked and saddened by the loss of life.”
The killings occurred on International Holocaust Remembrance Day, Jean-Pierre noted.
“The United States will extend our full support to the government and people of Israel,” she said.