The Israeli military said it had called up an unprecedented 300,000 reservists and was imposing a total blockade of the Gaza Strip, in a sign it may be planning a ground assault in response to the devastating weekend attack by Hamas gunmen.

After hours of intense bombardment by Israeli jets, Hamas, the Islamist movement which controls Gaza, said it would execute an Israeli captive if civilian houses were bombed.

Inside Israel, Palestinian fighters were still holed up in several locations, two days after they killed hundreds of Israelis and seized dozens of hostages in a raid that shattered Israel’s reputation of invincibility.