The Israeli raids early on Friday were the most intense in the occupied territory in months.
The first strike destroyed a pro-Hamas Islamic charity in Gaza City and a minute later, the helicopters fired at a cemetery in Khan Yunis fighters used as a launching pad to fire mortars at an adjacent Jewish settlement, witnesses said.
Palestinian resistance fighters fired shots into the air as crowds gathered at the site of the Gaza City blast. Ambulances raced to the scene.
Electricity was knocked out, and Palestinian police searched the building for a missile that apparently did not explode.
Dozens of people went into the street to watch despite the late hour - nearly 1am (2200 GMT Thursday).
Witnesses said one man was struck by flying debris in the Gaza City blast, but hospitals said they had no casualties yet.
Hamas expressed surprise at the
action of PA security forces
The Israeli army acknowledged one of the raids, saying it had struck an ammunition depot in Khan Yunis used by fighters of the resistance group Hamas.
The third raid was on a target in central Gaza, witnesses said.
There were no immediate reports of injuries in any of the raids which came hours after an Israeli woman was killed in the first deadly rocket assault from Gaza in months.
The Israeli army also cut off a key Gaza highway in two areas to restrict Palestinian travel in the area.
Abbas in Gaza
Amid the rise in tension and escalation in fighting, Palestinian President Mahmoud Abbas arrived in Gaza late on Thursday to meet leaders of the various resistance groups, reported Aljazeera.
Palestinian police and security forces in the Gaza Strip were placed on a state of alert due to "tension on the ground," a Palestinian interior ministry spokesman said.
Palestinian Authority (PA) Interior Minister, Nasr Yousif, had given the order after clashes erupted between PA security forces and a group from the al-Qassam Brigades, the military wing of the resistance movement Hamas.
"We have given clear and direct orders to all our security forces to do everything they can, including the use of force, to stop the firing of these homemade rockets out of Gaza and to prevent all these actions," he told reporters in Gaza.
Amid the rise in tension, Abbas
arrived in Gaza to meet fighters
A short time afterwards, a car ignored police orders to stop at a roadblock and police fired at it, wounding five, none seriously, officials said.
In a statement, the al-Qassam Brigades said they had fired 15 Qassam rockets and six mortar rounds at Israeli occupation targets in the area.
Five Palestinians were injured in the clashes. The Palestinian Interior Ministry declared a state of alert after the clashes.
Al-Aqsa Martyrs Brigades have also claimed responsibility for firing two of the rockets from Gaza, saying it was in retaliation to Israel's military operations which killed one of its members.
Hamas criticised the action of the Palestinian Authority's security apparatus, reported Aljazeera correspondent Wael al-Dahdouh.
A Hamas spokesman expressed surprised at the firing by the security forces against resistance fighters. "Instead of defending the Palestinian people against Israeli aggression, the Palestinian Authority is carrying out security duties on behalf of the enemy," the spokesman Mushir al-Misri said.
Aljazeera learned early on Friday that eight members of the National Reform Committee of the Palestinian Authority had offered their resignation to the Palestinian Prime Minister Ahmad Qureia.
The members attributed their move to what they termed a "lack of political will to activate the reform process and to implement the committee's decisions".