Thursday's Israeli bombardment was the heaviest so far
The Red Cross has accused Israel of failing to fulfil its obligation to help wounded civilians in Gaza.
ICRC staff found four weak and scared children beside their mothers' bodies in houses hit by shelling in Zeitoun.
The Israeli military has not yet responded to the accusation, but said it worked closely with aid groups so that civilians could get assistance.
Meanwhile the UN said it was suspending aid operations in Gaza because of the danger to staff from Israeli attacks.
"We have suspended our operations in Gaza until the Israeli authorities can guarantee our safety and security," said Chris Gunness, spokesman for the United Nations relief agency Unrwa.
"Our installations have been hit, our workers have been killed in spite of the fact that the Israeli authorities have the co-ordinates of our facilities and that all our movements are co-ordinated with the Israeli army.
"It is with great regret that Unrwa has been forced to make this difficult decision."
Earlier, Unrwa said one person had been killed and two injured when a fork-lift truck on a UN aid mission came under Israeli tank fire at Gaza's Erez crossing.
The Israeli military must have been aware of the situation but did not assist the wounded - neither did they make it possible for us or the Palestinian Red Crescent to assist the wounded
Pierre Wettach ICRC head for Israel and the Palestinian territories
Israel immediately responded with five artillery shells into Lebanon, calling it a "pinpoint response at the source of fire".
The rocket fire was condemned by Lebanon's prime minister.
The rocket attacks from Lebanon have raised concerns about a wider war in the region, says the BBC's Middle East Editor Jeremy Bowen.
In Gaza, Israel continued its offensive overnight with 60 air strikes targeting police sites, 10 Hamas tunnels, weapons storage facilities, launching pads "and a number of armed gunmen", the Israeli army said.
Casualty claims in Gaza have been difficult to verify independently.
While the BBC has had Palestinian producers reporting from Gaza, Israel only allowed Western TV crews to enter on Wednesday, embedded with its army.
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