Israeli air forces have targeted three training camps belonging to Hamas and the Islamic Jihad group in retaliation for rockets fired at the city of Ashkelon and the town of Netivot from the Gaza Strip.
The aerial bombings, which took place before dawn, caused some damage but no casualties according to witnesses. The Israeli Defense Force (IDF) confirmed the raids saying that it "struck three terror infrastructures in the Gaza Strip" and "hits were confirmed".
Earlier, the IDF reported that sirens went off in Ashkelon and Netivot in the second rocket launching in a week.
Israeli defence officials said the militants who fired the rockets belong to a "rogue group".
A radical Islamist Salafist group, which calls itself the Omar Brigades, claimed responsibility for firing three rockets from Gaza saying it was in retaliation for Hamas' killing of an Islamic state (Isis) supporter in the Palestinian territory.
"We are continuing with our jihad against the Jews, the enemies of God and no one will be able to deter us," it said.
The IS supporter, a 27-year-old militant named as Younis al-Honnor, was killed during an attempt to arrest him, according to Hamas spokesman Eyad al-Bozum. He reportedly refused to surrender and Hamas security forces opened fire in the house where he was holed up.
Israeli defence minister Moshe Ya'alon said Israel "holds Hamas responsible for what is happening in the Strip". "We will not tolerate attempts to hurt our citizens," he said. "We will strike harder if we have to, and last summer has proven that."
Before the Israeli air strikes, Hamas security services evacuated their headquarters in the Strip for fear of an Israeli response.
The escalation threatens an Egyptian-brokered truce signed last August between Israel and Hamas that ended Israeli offensive in the Gaza Strip.