Israeli aircraft pounded Hamas government buildings in Gaza on Saturday, including the building housing the prime minister's office, after Israel's Cabinet authorised the mobilisation of up to 75,000 reservists, preparing the ground for a possible invasion into Gaza.

Hamas, the Islamist group that runs the Gaza Strip, said Israeli planes bombed the office building of Prime Minister Ismail Haniyeh - where he had met on Friday with the Egyptian prime minister, and struck a police headquarters building.

An Israeli military spokeswoman confirmed the strike on Haniyeh's office.

On Friday, Palestinians fired a rocket toward Jerusalem for the first time in decades.

Tel Aviv, Israel's commercial centre, also came under rocket attack for the second straight day, in defiance of an Israeli air offensive that began on Wednesday with the declared aim of deterring Hamas from launching cross-border attacks that have plagued southern Israel for years.

Hamas claimed responsibility for firing at Jerusalem and Tel Aviv. Israel said the rocket launched toward Jerusalem landed in the occupied West Bank, and the one fired at Tel Aviv did not hit the city. There were no reports of casualties.

The siren that sounded in Jerusalem stunned many Israelis. The city, holy to Jews, Muslims and Christians, was last struck by a Palestinian rocket in 1970, and it was not a target when Saddam Hussein's Iraq fired missiles at Israel in the 1991 Gulf War.

Prime Minister Benjamin Netanyahu held a four-hour strategy session late on Friday with a clutch of senior ministers in Tel Aviv on widening the military campaign, while other Cabinet members were polled by telephone on raising the mobilisation level.

Political sources said they decided to more than double the current reserve troop quota set for the Gaza offensive to 75,000. The move did not necessarily mean all would be called into service.

Hours earlier, Egypt's prime minister, denouncing what he described as Israeli aggression, visited Gaza and said Cairo was prepared to mediate a truce.

U.S. President Barack Obama spoke with Netanyahu and Egyptian President Mohamed Mursi on Friday, the White House said.

Officials in Gaza said 30 Palestinians - 14 militants and 16 civilians, a mong them eight children and a pregnant woman - had been killed in the enclave since Israel began its air strikes. Three Israeli civilians were killed by a rocket on Thursday.

The Israeli military said 133 rockets fired from Gaza had hit Israel since Friday and 82 more were intercepted by its Iron Dome anti-missile system. Dozens of Israeli bombing raids rocked the enclave.

In a further sign Netanyahu might be clearing the way for a ground operation, Israel's armed forces announced that a highway leading to the territory and two roads bordering the enclave of 1.7 million Palestinians would be off-limits to civilian traffic.

Tanks and self-propelled guns were seen near the border area on Friday, and the military said it had already called 16,000 reservists to active duty.

Netanyahu is favoured to win a January national election, but further rocket strikes against Tel Aviv, a free-wheeling city Israelis equate with New York, and Jerusalem, which Israel regards as its capital, could be political poison for the conservative leader.

"The Israel Defence Forces will continue to hit Hamas hard and are prepared to broaden the action inside Gaza," Netanyahu said before the rocket attacks on the two cities.

Asked about Israel massing forces for a possible Gaza invasion, Hamas spokesman Sami Abu Zuhri said, "The Israelis should be aware of the grave results of such a raid, and they should bring their body bags."-Reuters