Palestinian men inspect the site of an Israeli military strike in Gaza City on July 8, 2014
Jerusalem (AFP) - Hamas militants in the Gaza Strip fired missiles at Jerusalem and Tel Aviv Tuesday after Israel killed 21 Palestinians on the first day of a major campaign to stamp out rocket fire.
It was the most serious flare-up over Gaza since November 2012 and came as Israel was struggling to contain a wave of violence at home over the grisly murder of a Palestinian teenager by Jewish extremists.rocket attacks on
After a day in which Israel staged multiple air strikes on Gaza, leaving 17 people dead and more than 100 wounded, militants from the Islamist movement Hamas hit back with rocket fire on Israel's major population centres in Jerusalem and Tel Aviv.
As sirens wailed across the Holy City, three loud explosions were heard and a series of flashes light the sky to the southwest.
A tweet from the Israeli military said "Confirmed: A rocket fired from Gaza hit Jerusalem, Israel’s capital city."
"Until now, one hit has been identified in an open area near Ramat Raziel," police spokeswoman Luba Samri said, adding there were no reports of injuries of damage anywhere in the Jerusalem area.
The attack was claimed by the Ezzedine al-Qassam Brigades, the armed wing of Hamas, which said it had fired "four M75 rockets" at Jerusalem, which lies 65 kilometres (40 miles) from the Palestinian enclave.
It also claimed to have launched a rocket at Haifa, 165 kilometres (100 miles) away, although there was no confirmation of anything hitting the northern port city.
Hamas also claimed firing four rockets at Tel Aviv, which lies 60 kilometres north of Gaza, with sirens wailing across the city.
Earlier, another rocket aimed at the coastal city was shot down by the Iron Dome anti-missile defence system.
There were no immediate reports of casualties.
Palestinian president Mahmud Abbas has demanded Israel "immediately stop" its air campaign and called on the international community to pressure the Jewish state.
But after nearly four weeks of intensifying rocket fire, Israel appeared bent on dealing the Islamist Hamas movement a heavy blow, with the cabinet authorising the call-up of some 40,000 reservists.
In the worst strike of the day, a missile slammed into a house in the southern Gaza city of Khan Yunis killing eight people and wounding 25, emergency services spokesman Ashraf al-Qudra said.
Witnesses said an Israeli drone fired a warning flare, prompting relatives and neighbours to gather at the house as a human shield.
But an F-16 warplane fired a missile that levelled the building.
Hamas denounced the attack as "a horrendous war crime" and said it would retaliate against "all Israelis."
- Battle on the beach -
Shortly afterwards, troops killed four Hamas militants who reached the Israeli coast by sea and attacked an army base near Zikim, a military official said.
"A number of terrorists came out of the ocean and attacked... with Kalashnikov rifles and hand grenades," said Lieutenant Colonel Peter Lerner, who said they were all killed.
The attack was claimed by the Qassam Brigades.
Hamas militants also claimed to have fired 10 rockets at two army bases.
Several hours earlier, two people were killed in a strike east of Gaza City, the emergency services said.
Two more people died in separate strikes, one of which hit a motorised rickshaw in the northern town of Beit Lahiya, while a second killed a 16-year-old boy in Gaza City.
Earlier, three people were killed in a strike on a car in central Gaza City. Relatives said all three were Hamas militants, with one identified as a senior figure responsible for the armed wing's naval unit.
Another man was killed in central Gaza, with witnesses saying he was also a Hamas militant.
- Ground assault? -
Meanwhile, the military was preparing all options to stamp out rocket fire from Gaza, "including an invasion or a ground operation," a senior Israeli official said.
Military spokesman General Moti Almoz confirmed preparations for a possible ground offensive, telling army radio "we have been instructed by the political echelon to hit Hamas hard."
"All options are on the table; all these steps are being considered," he said indicating that two brigades were already stationed around Gaza, with more to join them in the coming days.
Also on Tuesday, the army said the cabinet approved the call-up of 40,000 reservists.
"We are preparing for a campaign against Hamas, which will not end in just a few days," Defence Minister Moshe Yaalon said in a statement.
Since June 12, when the current round of tit-for-tat violence began, more than 250 rockets have hit southern Israel, with another 40 intercepted by Iron Dome.
So far no Israelis have been killed.
The US State Department said it "strongly condemns" the rocket fire, and backed "Israel’s right to defend itself against these attacks," a spokeswoman said.
And the EU ambassador to Israel, Lars Faaborg Andersen, expressed "unreserved solidarity" with Israelis living in the south.
British Foreign Secretary William Hague also urged Hamas to halt its attacks, while Turkey called for an immediate end to the Israel assault.
The Arab League, meanwhile, called for an urgent UN Security Council meeting on the crisis.