Israel has bombarded the Hamas-ruled Gaza Strip with about 300 airstrikes and shot down a Palestinian rocket fired at Tel Aviv, the military said.
The strikes widened a blistering assault to include the Hamas prime minister's headquarters, a police compound and a network of smuggling tunnels.
The intensified airstrikes came as Egyptian-led attempts to broker a ceasefire and end Israel's four-day-old Gaza offensive gained momentum. The leaders of Hamas and two key allies, Qatar and Turkey, were in Cairo for talks with Egyptian officials, and the Arab League was holding an emergency meeting.
The White House said President Barack Obama was also in touch with the Egyptian and Turkish leaders. The US has solidly backed Israel so far. Speaking on Air Force One, deputy national security adviser Ben Rhodes said that the White House believes Israel "has the right to defend itself" against attack and that the Israelis will make their own decisions about their "military tactics and operations".
The Israeli attacks, which Gaza officials say left 12 dead, came as Palestinian militants fired more than 100 rockets towards Israel, including two aimed at the commercial and cultural centre of Tel Aviv.
Rocket attacks on Tel Aviv and Jerusalem this week mark the first time Gaza militants have managed to fire rockets towards the cities, raising the stakes in the confrontation. The widened scope of targets brings the scale of fighting closer to that of the war the two groups waged four years ago.
In a psychological boost for the Israelis, a sophisticated Israeli rocket-defence system known as "Iron Dome" knocked down one of the rockets headed towards Tel Aviv, eliciting cheers from relieved residents huddled in fear after air raid sirens sounded in the city. Video footage showed a plume of smoke rising from a rocket-defence battery deployed near the city, followed by a burst of light overhead. The smoke trailed the intercepting missile.
Israel opened the offensive on Wednesday with a surprising airstrike that killed Hamas' military chief, then attacked dozens of rocket launchers and storage sites. It says the offensive is meant to halt months of rocket fire on southern Israel.
While Israel claims to be inflicting heavy damage on Gaza's Hamas rulers, it has failed to slow the rocket fire. In all, 42 Palestinians, including 13 civilians, have been killed, while three Israeli civilians have died.
Israel has authorised the call-up of as many as 75,000 reservists ahead of a possible ground operation. Dozens of armoured vehicles have massed along the border with Gaza in recent days.
www.idf.il/english/ (Israel Defence Forces)