Up to 20 people have been killed in the deadliest night of Israeli air raids on Gaza since its current offensive began, Palestinian sources say.
Most occurred in attacks on a house and a cafe in the south, they say.
Militants in Gaza continued firing rockets into Israel on Thursday, with sirens sounding over southern towns.
UN Secretary General Ban Ki-moon warned the situation in Gaza was "on a knife-edge", urging Israel and Palestinian militants to end hostilities.
The deaths overnight take the number of Palestinians killed since Israel launched its Operation Protective Edge on Tuesday to more than 60.
'Tap on roof'
The Israeli military said that it had attacked 108 targets since midnight and that 12 rockets had been fired at Israel, seven of them intercepted by the Iron Dome defence system.
The site of an Israeli strike in Gaza City.
Palestinian sources say the cafe in Khan Younis was hit while people were watching the world cup semi-final on television. First reports say that nine people died in that attack.
Separately, eight Palestinians were killed in an air strike on a house near the city, the Palestinian health ministry said.
Israel has not commented on the incidents.
Elsewhere on Thursday, three people also died in an Israeli strike on a car in western Gaza City, Palestinian reports say.
Militant rocket fire into Israel continued on Thursday, with sirens sounding in Ashkelon and other southern Israeli areas.
The armed wing of Hamas said it had fired two M75 rockets at Tel Aviv.
An Israeli military spokesman however said an attack on a house in Khan Younis on Tuesday in which eight people were killed was "a tragedy - not what we intended", adding people had returned to the building too soon following a telephone warning.
The home was said to be that of Odeh Kaware, a local Hamas commander.
Israeli sources say a warning was given of an imminent attack and a projectile without a warhead was then fired at the building in a second warning move sometimes called "the tap on the roof".
But they say people began returning to the building in the time between the firing of that warning shot and the firing of the explosive missile.
Overnight Mr Ban warned of the dangers of escalation, saying the region "cannot afford another full-blown war".
"The deteriorating situation is leading to a downward spiral which could quickly get out of control," Mr Ban said. "The risk of violence expanding further still is real."
He demanded that Hamas militants stop firing rockets and also urged the Israeli government to exercise restraint and respect international obligations to protect civilians.
The UN Security Council is due to meet for emergency talks on the crisis later on Thursday.
Israeli PM Benjamin Netanyahu earlier vowed to "further intensify attacks on Hamas" in Gaza, saying the militants would "pay a heavy price" for their rocket attacks.
Mustafa Barghouti, a member of the Palestinian Legislative Council, accused Mr Netanyahu of "preparing a ground operation which could bring a huge massacre in Gaza".
He told the BBC that Hamas was ready for a mutually declared ceasefire, but that Israel had rejected a truce. "Mr Netanyahu seems determined to continue this terrible war," Mr Barghouti said.
Israeli President Shimon Peres told CNN that a ground offensive might happen "quite soon". The army has called up about 40,000 reservists.
Hamas said that all Israelis were now targets, accusing Israel of violating the Egyptian-brokered truce that ended exchanges in 2012.
The leader of Hamas' political bureau, Khaled Meshaal, warned that Hamas would continue to retaliate and called on Palestinians to unite.
Last month, Hamas and Palestinian President Mahmoud Abbas agreed to form a unity government to end a major rift between their factions in the West Bank and Gaza.
Israel suspended crisis-hit peace talks with the Palestinians in April in response to the announcement of the reconciliation deal with Hamas, which it regards as a terrorist organisation.
un secretary general, ban ki moon, out of control, un security council, up to, the south, secretary general, world cup, health ministry, tel aviv, to be, out of, exercise restraint, the un, security council
TB rates in children 'much higher than WHO estimates'(09:50 10/07/2014)
Smart LED light bulbs leak wi-fi passwords(08:19 10/07/2014)
Indonesians vote in tight presidential race(14:43 09/07/2014)
Lessons in girl power in Ghana's schools(14:43 09/07/2014)
Alzheimer's research in 'major step' towards blood test(10:40 09/07/2014)
Japan braced for Typhoon Neoguri(10:40 09/07/2014)
South Korea ferry 'sank due to negligence, corruption'(10:40 09/07/2014)
Afghan crisis: Nato troops among 16 dead in Bagram bombing(10:40 09/07/2014)
India building collapse rescue ends with 61 dead(13:28 07/07/2014)
US enhanced airport security checks target electronics(12:33 07/07/2014)
Ukraine says forces retake two more rebel-held cities(11:02 07/07/2014)
Wastewater from energy extraction 'triggers US quake surge'(08:57 05/07/2014)