Two weapons storage facilities and a rocket-launching site in Gaza were targeted by the Israeli Air Force in the early hours of Monday morning, the IDF Spokesperson’s office said, after at least six rockets were launched from the Strip into southern Israel late Sunday night and early Monday.

“The IDF will not tolerate attempts to harm Israeli citizens, and our soldiers will continue to act against anyone who engages in terror against the State of Israel. The Hamas terror organization is held responsible,” the IDF said in a statement.

Hamas reportedly evacuated its headquarters and several security facilities overnight for fear of IAF strikes

On Monday morning, Defense Minister Moshe Ya’alon ordered the closure of the Kerem Shalom and Erez border crossings to Gaza, in response to the rocket fire.

Red alert sirens sounded across several regions of southern Israel, in the worst such attacks since last November. There were no reports of injuries or damage.

Four of the rockets exploded in open areas near Netivot and the Bnei Shimon region, west of Beersheba. The Iron Dome system intercepted two of the projectiles, believed to have been Grad rockets. Sirens were also heard near the Beduin town of Rahat in the Negev and in the Ashkelon Regional Council.

The IDF said that the rockets had likely been launched from the northern Gaza Strip.

The IDF was checking the possibility that the rockets were launched by radical Salafi fighters who do not recognize Hamas rule, or as an act of defiance by the terrorist group Islamic Jihad, which earlier Sunday announced that it was suspending ties with the ruling Hamas government.

The rift came after a confrontation Saturday between Hamas policemen and a senior Islamic Jihad member that the police were trying to take into custody for interrogation. The suspect was killed in the standoff, with Hamas alleging that he had committed suicide.

“Islamic Jihad today suspended its contacts with Hamas after police opened fire yesterday on one of the commanders of the Al-Quds Brigades, Raed Jundiya, 38, inflicting serious injuries from which he died this morning,” AFP quoted a leader of the extremist group as saying.

“The murder of Raed Jundiya represents a major service to the Zionist enemy, provided completely free of charge, whether deliberately or not, because the martyr was, as everybody knows, on the top of the Zionists’ hit-list as he headed the Brigades’ rocket unit,” he said.

The extremist group boasts some 8,000 members of its military wing, making it the second largest armed group in the Gaza Strip. Islamic Jihad has largely respected the Egyptian-brokered agreement that brought to an end Operation Pillar of Defense last November.

Sunday’s incident represents the first time rockets have hit the Netivot and Bnei Shimon areas since the end of the military operation.

Last week, The Times of Israel reported that Hamas had deployed a 600-man force in Gaza to prevent rocket fire at Israel.