Gaza- 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 at least 70, Palestinian officials say.

Israel says its targets have been militant fighters and facilities including rocket launchers, weapons stores, tunnels and command centres.

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.

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. Reports said the victims were militants from Islamic Jihad.

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.

Separately, Egyptian state television said the government had decided to open the Rafah border crossing on Thursday to evacuate some of those wounded in the Israeli attacks.

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