Plumes of black smoke wafted into Gaza City's skies following at least five airstrikes, in atmosphere reminiscent of Israel's large scale 2008-2009 attack on Gaza. Ambulance sirens blared as people ran in panic in the streets and militants fired angrily into the air.
Outside the hospital where Jabari's body was taken, Hamas official Khalil al-Haya eulogized Jabari and threatened Israel.
"The battle between us and the occupation is open and it will end only with the liberation of Palestine and Jerusalem," an emotional al-Haya said.
Outside the hospital, thousands of angry Gazans chanted "retaliation" and "we want you to hit Tel Aviv tonight."
The Israeli military said the assassination was just the beginning.
"After a couple of days on ongoing rocket attacks toward Israeli civilians the (Israeli military) chief of staff has authorized to open an operation against terror targets in the Gaza Strip," military spokeswoman Lt. Col. Avital Leibovitch said.
She said Jabari had "a lot of bloods of his hands" and that the military chief "authorized different targets" as well.
Shortly after, she said Israeli aircraft targeted 20 locations in Gaza that served as storage or launching sites for rockets. Among the weapons destroyed were rockets that could hit as far as 40 kilometers (25 miles) into Israel.
Advocates say targeted killings are an effective deterrent without the complications associated with a ground operation, chiefly civilian and Israeli troop casualties. Proponents argue they also prevent future attacks by removing their masterminds.
Critics say the killings invite retaliation by militants and encourage them to try to assassinate Israeli leaders. They complain that the strikes amount to extrajudicial killings.
Dovish Israeli lawmaker Dov Hanin condemned the killing.
"Assassinating leaders is never the solution. In place of the leaders killed, other will grow, and we will only get another cycle of fire and blood," he said.