JERUSALEM (AFP)— Israel imposed a total siege on the Gaza Strip Monday and cut off the water supply as it kept bombing targets in the crowded Palestinian enclave in response to the Hamas surprise assault it has likened to the 9/11 attacks.

Reeling from the Islamist group’s unprecedented ground, air and sea attacks, Israel has counted over 700 dead and launched a withering barrage of strikes on Gaza that have killed 560 people there.

The skies over Gaza were blackened by plumes of smoke from deafening explosions as Hamas kept launching rockets as far as Tel Aviv and Jerusalem, where missile defence systems fired and air raid sirens blared.

Hamas — whose militants surged into Israeli towns on Saturday, spraying gunfire at civilians and dragging off about 100 hostages — claimed on Monday that Israeli air strikes had killed four of the captives.

Israel said it had called up 300,000 army reservists for its “Swords of Iron” campaign, and truck convoys were moving tanks to the south, where its forces had dislodged the last holdout Hamas fighters from embattled towns.

“We are in control of the communities,” said military spokesman Daniel Hagari, cautioning that some “terrorists” may remain after about 1,000 militants had swarmed into the region on the Jewish Sabbath.

Defence Minister Yoav Gallant said Israel would impose a “complete siege” on the long blockaded enclave and stressed what this meant for its 2.3 million people: “No electricity, no food, no water, no gas — it’s all closed.”

Palestinians in the impoverished coastal territory braced for what many feared will be a massive Israeli ground attack aiming to defeat Hamas and liberate the hostages.

Israel Prime Minister Benjamin Netanyahu has warned Gaza civilians to get away from all Hamas sites, which he vowed to turn “to rubble”.

Middle East tensions have spiked as Israel’s arch enemy Iran and their Lebanese ally Hezbollah have praised the Hamas attack, although Tehran rejected any role in the military operation.

Hamas has called on “resistance fighters” in the occupied West Bank and in Arab and Islamic nations to join its “Operation Al-Aqsa Flood”, launched half a century after the 1973 Arab-Israel war.

“The military operation is still continuing,” Hossam Badran, a Hamas official, told AFP from Doha, adding that “there is currently no chance for negotiation on the issue of prisoners or anything else”.

The United States has pledged “rock solid” support for Israel and said it would send munitions and military hardware to its key ally and divert an aircraft carrier group to the eastern Mediterranean.

Israel, which has long prided itself on a high-tech military and intelligence edge in its many conflicts, has been shaken to the core by Hamas’s unprecedented attack.

It now faces the threat of a multi-front war after Hezbollah launched guided missiles and artillery shells from the north on Sunday “in solidarity” with Hamas, in what some observers considered a warning shot.

On Monday, the Israeli army said its soldiers had “killed a number of armed suspects” who had crossed the border from Lebanon and that Israeli helicopters were striking targets in the area.