(UPI) -- The commander of the al-Qassam Brigades, Hamas' military wing, was killed Wednesday in an Israeli airstrike on Gaza, the group said.

Hamas said an Israeli missile hit the car in which Ahmed al-Jaabari was riding, the Ma'an news agency reported. The Israeli intelligence agency Shin Bet said the strike was justified by Jaabari's "decade-long terrorist activity."

"The purpose of this operation was to severely impair the command and control chain of the Hamas leadership, as well as its terrorist infrastructure," Israeli military sources told Ma'an.

The attack ended an apparent truce negotiated by Egypt. Israeli Brig. Gen. Yoav Mordechai said the country should be prepared for "protracted" conflict in the south as the military said it had rockets aimed at Hamas sites.

Militant Palestinian groups in Gaza reacted angrily.

"Cowardly settlers had better flee to shelters where we will bury them and they will never be able to leave," Abu Mujahid, a spokesman for the Popular Resistance Committees, told Ma'an. "The occupation has started the battle and we will respond very fiercely to their crimes."