Israeli destroys Prime Minister Ismail Haniya's headquarters as the country launches 200 airstrikes at targets in Gaza.

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Israel's cabinet was mobilising up to 75,000 reservists on Saturday, preparing the ground for a possible invasion, although Israeli officials insisted that no decisions had yet been taken.

The mobilisation followed reports that Palestinians fired a rocket toward Jerusalem for the first time in decades, with Hamas claiming responsibility. There were no casualties.

The widened scope of targets brought the scale of fighting closer to that of the war the two groups waged four years ago when Hamas was badly bruised. Hamas has since restocked its arsenal with more and better weapons, however, and has been under pressure from smaller, more militant groups to prove its commitment to fighting Israel.

Attack on Tel Aviv

Israel reported that a rocket landed in the occupied West Bank on Saturday. Tel Aviv and Israel's commercial centre came under rocket attack for the second straight day, in defiance of an Israeli air offensive that began on Wednesday.

There were differing reports of casualties. Gaza health official Ashraf al-Kidra said 39 Palestinians including 13 civilians and three Israeli civilians have died since Wednesday.

In addition to calling up thousands of reservists and troops, Israel amassed tanks and other armoured vehicles along the border with Gaza and announced that a highway leading to the territory and two roads bordering the enclave of 1.7m Palestinians would be off-limits to civilian traffic.

Israel's blistering attack overnight targeted key facilities in Gaza including a stadium and the prime minister's office on the fourth day of Israeli air strikes in the coastal enclave.

Jabaliya refugee camp strike

The strikes also targeted the home of a Hamas leader in the densely populated Jabaliya refugee camp near Gaza City. Some reports said missiles may have gone through the front room. critically wounding him and injuring other residents of the building.

A high-level Tunisian delegation, led by Foreign Minister Rafik Abdessalem, defied the fighting to arrive in Gaza on Saturday. Their first stop was the smouldering ruins of the prime minister's demolished headquarters. Mr Haniyeh's three-story office building was flattened by an airstrike that blew out windows in neighboring homes. He was not inside the building at the time.

It was the first official Tunisian visit since Hamas's violent 2007 takeover of the territory. Egypt's prime minister visited Friday and a Moroccan delegation is due on Sunday, following a landmark visit by Qatar's leader last month that implied political recognition.

Missiles smashed into two small security facilities and the massive Hamas police headquarters in Gaza City, setting off a huge blaze that engulfed nearby houses and civilian cars parked outside, the Interior Ministry reported. No one was inside the buildings, The Associated Press reported.

Air attacks knocked out five electricity transformers, cutting off power to more than 400,000 people in southern Gaza, according to the Gaza electricity distribution company.