Hamas, which rules Gaza, said Israel had “opened the gates of hell” when it targeted the group’s training facilities and rocket launchers.

Qatar, which has emerged as the strongest Arab supporter of Hamas, said Israel’s offensive “should not pass without a punishment”.

Israel moved additional infantry troops to the south, near its border with Gaza, and called up some units of reservists to have them on standby.

Israeli Prime Minister Benjamin Netanyahu said the Israeli Defence Forces were prepared to “broaden the operation”.

“Today we relayed a clear message to the Hamas organisation and other terrorist organisations,” Mr Netanyahu said. “And if there is a need, the IDF is prepared to broaden the operations. We will continue to do everything in order to protect our citizens.”

British Foreign Secretary William Hague said Hamas “bears principal responsibility’’ for the current crisis in Gaza, saying it should cease attacks against Israel immediately.

His comment came as the death toll hit 13 in 20 hours of Israeli air strikes, which also left at least 120 people injured, medics said. In the same period, Gaza rockets killed three Israelis and injured another five in a direct hit on a residential building in the southern town of Kiryat Malachi, police said.

Hague also strongly urged Israel to do its “utmost’’ to reduce tensions, avoid civilian casualties and help create the conditions for peace, warning: “It is imperative to avoid the risk of a spiral of violence.’’

Since the violence erupted when Israel killed a top Hamas militant on Wednesday afternoon, the military has carried out “around 150 strikes’’ on Gaza, a spokeswoman said.

In the same period, “at least 195 rockets’’ hit Israel while another 48 were intercepted by the Iron Dome anti-missile system.

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