"The aim of targeting these sites is to hamper their rocket-launching weapons build up capabilities," the IDF statement said, adding that the Gaza strip had become "a frontal base for Iran firing rockets and carrying out terrorist attacks against Israeli citizens."
Angry crowds gathered at the heavily damaged vehicle that contained the bodies of al-Ja'abari and his bodyguard.
Saeb Erakat, the chief Palestinian negotiator, condemned "in the strongest possible terms" what he called the Israeli assassination of al-Ja'abari.
In an interview with CNN, Erakat labeled the attack the beginning of a "major, major Israeli escalation," and he called on the international community to pressure Israel to halt its operation.
Al-Mukhalalati, the Gaza health minister, also called on "the free world to stop this massacre committed by Israel."
Asked about assassinating al-Ja'abari, Regev said the Hamas military leader headed a "terror military machine."
"This is the man with blood on his hands. This man is a known and wanted terrorist," he said. "In taking him out, Israel was acting legitimately."
The latest escalation in violence is part of a cycle of attacks between periods of relative stability between Israel and the Palestinians.
"This was both inevitable and predictable," said Aaron David Miller, a Middle East expert and vice president at the Woodrow Wilson Center.
There is no long-term basis for both sides to find a lasting peace, he said.
Israel and the Palestinians have "completely different political and strategic goals," Miller explained. The focus should be on how to bring security until a basis for long-term stability arises, he added.