Gaza militants fired missiles at Jerusalem and Tel Aviv on Tuesday after Israel killed 27 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 struggled to contain a wave of violence at home over the grisly murder of a Palestinian teenager by Jewish extremists.
After a day in which Israel staged multiple air strikes on the Gaza Strip, which also left 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 lit the sky to the southwest.
Local witnesses told AFP they heard a blast in Ramat Raziel, some 10 kilometres (six miles) from the city's southwestern flank.
"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 in the Jerusalem area.
The rocket 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.
There was no report of anything hitting the northern port city but the army said a rocket did fall in Hadera, 100 kilometres (62 miles) north of Gaza.
Hamas militants also said they fired four rockets at Tel Aviv, 60 kilometres north of Gaza, setting sirens off across the city. Earlier, another rocket aimed at Israel's commercial capital was shot down by the Iron Dome anti-missile defence system.
- Family home hit -
Palestinian president Mahmud Abbas has demanded Israel "immediately stop" its air campaign and called on the international community to pressure the Jewish state.
"The Palestinian Authority will go to all international organisations to seek protection for the Palestinian people," he said in a televised statement late Tuesday night.
But after nearly four weeks of intensifying rocket fire, Israel appeared bent on dealing the Islamist Hamas movement a heavy blow.
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 at the building, levelling it.
Hamas denounced the attack as "a horrendous war crime" and vowed retaliation against "all Israelis".
Another strike, on a house in Beit Hanoun, in the north of the strip, killed six people, Qudra said, without giving details.
Altogether, the Israeli air raids left 23 people dead, including an eight-year-old boy and two teens.
Among those killed were a local Islamic Jihad commander and three Hamas militants, including a senior member of Hamas's armed wing, the Ezzedine Al-Qassam Brigades.
In addition, Israeli troops killed four Hamas militants who reached the Israeli coastline by sea and tried to attack an army base near Zikim.
"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.
- 40,000 reservists mobilised -
"Israel will not tolerate the firing of rockets on our cities and towns," Israeli Prime Minister Benjamin Netanyahu said late on Tuesday.
"We have therefore significantly expanded our operations against Hamas and the other terrorist organisations in Gaza ... Israel is not eager for war, but the security of our citizens is our primary consideration," he said in a statement.
His remarks came after the security cabinet approved the call-up of some 40,000 reservists, as a senior official told AFP the military was preparing all options to stamp out the rocket fire, "including an invasion or a ground operation".
"All options are on the table; all these steps are being considered," said military spokesman General Moti Almoz in an interview with army radio in which he said two brigades were already stationed around Gaza, with more to join them in the coming days.
"We have been instructed by the political echelon to hit Hamas hard."
Since June 12, when the current round of tit-for-tat violence began, the army says hundreds of rockets have hit southern Israel, with another 40 intercepted by Iron Dome. So far, no Israelis have been injured or killed.
Washington condemned the rocket fire an the "deliberate targeting of civilians" by militants and the European Union also denounced the "indiscriminate" fire from Gaza and the "growing number of civilian casualties... caused by Israeli retaliatory fire" and demanded an immediate ceasefire.
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.
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