An Israeli air attack has killed 12 members of one family in the Gaza Strip, just hours after Binyamin Netanyahu, Israeli prime minister, said his country was ready to "significantly expand" its operation against Palestinian fighters in the territory.
Barack Obama, the US president, said that while Israel had a right to defend itself, it would be "preferable" to avoid an Israeli ground invasion.
Sunday's 30 deaths in Gaza, including the deaths of seven civilians on Monday, have brought the total number of Palestinians killed to 82 since the Israeli air strikes began targeting the Hamas-ruled territory six days ago.
On their part, fighters in Gaza continued to fire rockets into Israel. Two of them, aimed at the commercial hub of Tel Aviv, were shot down by Israel's anti-missile system, police said.
"The operation in the Gaza Strip is continuing, and we are preparing to expand it," Netanyahu said at the weekly cabinet meeting on Sunday.
"We are extracting a heavy price from Hamas and the terror organisations."
Meanwhile, thousands of Israeli troops backed by armour massed along the Gaza border, fuelling fears that Israel is poised to expand its aerial bombing campaign into a ground operation.
Ashraf al-Kidra, spokesperson of the health ministry in Gaza, said on Sunday that civilians accounted for half of the Palestinian death toll. More than 750 other Palestinians have been wounded.
In the single deadliest attack of the Israeli operation so far, 12 civilians were killed in Sunday's air attack on a four-storey house in northern Gaza City, health officials said.
Two or three missiles fired by F-16 fighter jets reduced the house in the Sheikh Radwan neighbourhood to rubble, witnesses said.
Five women, including one 80-year-old, and four small children were among the dead, Kidra said.
The Israeli military said the target was a top rocket mastermind of the Islamic Jihad group. The claim could not be verified, and Kidra said the two men killed in the attack were also civilians.
Earlier, medical sources in Gaza said at least three children - including an 18-month-old infant - and two women were killed in a air raid east of Bureij refugee camp in central Gaza.
An air raid before dawn in Gaza City targeted a building housing the offices of local Arab media, wounding several journalists from al-Quds television.
"At least six journalists were wounded, with minor and moderate injuries, when Israeli warplanes hit the Al-Quds TV office in the Showa and Housari building in the Rimal neighbourhood of Gaza City," Ashraf al-Qudra, health ministry spokesman, told AFP news agency.
He said one journalist lost his leg.
Witnesses reported extensive damage to the building, and said journalists had evacuated after an initial strike, which was followed by at least two more on the site.
A second media centre was targeted later on Sunday morning. Sky News, Al-Arabiya and the official Hamas-run Al-Aqsa TV channel have offices in the building.
Russian television station RT said its office was destroyed, adding that none of its staff were injured.
The Israeli military said it had targeted "two Hamas operational communication sites" and had only targeted communication devices located on the roof to "minimise the damage to non-involved persons".
Huge plumes of smoke were billowing in the sky after a security building in Gaza City was hit.
Two other attacks on houses in the Jabalya refugee camp killed one child and wounded 12 other people, medical officials said.
Hamas remained defiant, however, with Abu Ubaida, its military spokesperson, insisting that despite Israel's blows the group "is still strong enough to destroy the enemy".
"This round of confrontation will not be the last against the Zionist enemy and it is only the beginning," he said on TV.
Gaza has been under attack since Wednesday, when Israel launched a military offensive with the declared goal of deterring fighters in the Palestinian enclave from launching rockets into its territory.
During this period, more than 500 rockets fired from Gaza have hit Israel, killing three people and injuring dozens.
Al Jazeera's Nadim Baba, reporting from Gaza City, said some people who live near the northern and eastern borders with Israel had been leaving their homes to seek shelter with relatives elsewhere.
In Gaza City, streets were relatively quiet on Sunday.
"People still do think that the Israeli military might actually launch a ground incursion," he said.
"They are of course also worried that they might be near targets of the Israeli military, and they might also be near to a place from where rockets are being launched."
Our correspondent witnessed a rocket being launched from a waste ground in the city. "Then I saw civilians running away from that area," he said.
Rocket fire from Gaza into Israel subsided during the night but resumed in the morning with at least 50 rockets fired, the Israeli army said.
At least 17 of them were intercepted by the so-called Iron Dome, Israel's a missile-defence system meant to shoot down rockets and artillery shells fired at populated areas.
Two people were lightly injured by a rocket hitting a house in the coastal city of Ashkelon, the Magen David Adom emergency services said.
The military said Israeli aircraft had targeted dozens of underground rocket launchers overnight, "causing severe damage to the rocket launching capabilities of Hamas and other terror organisations".
It also confirmed that its navy had shelled Gaza, hitting targets on the northern Gaza shore line.
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Netanyahu told the Sunday cabinet meeting that he was holding talks with world leaders, "and we appreciate their understanding of Israel's right to self-defence".
Al Jazeera's Hoda Abdel-Hamid, reporting from Sderot in southern Israel, said the Israeli leader had a lot of support for a ground operation, especially in the southern parts of the country.
However, a ground invasion would cost Israel much international sympathy and support, according to William Hague, UK foreign secretary.
Hague told Sky News television it was much more difficult to limit civilian casualties in a ground assault and it would threaten to prolong the conflict.
"A ground invasion is much more difficult for the international community to sympathise with or support - including the United Kingdom," he said.
Hague said Britain would like to see an agreed ceasefire, with an end to the rocket attacks being an essential component of any peace deal.
Ghazi Hamad, a Hamas spokesperson, has told Al Jazeera that 90 per cent of the terms of a ceasefire currently being discussed in the Egyptian capital, Cairo, have been agreed upon.