Palestinians gather around the remains of a house, which witnesses said was destroyed in an Israeli air strike, in Gaza City

AFP/Gaza City

Hamas executed 18 alleged collaborators in Gaza City on Friday as Israeli Prime Minister Benjamin Netanyahu vowed harsh retribution for the killing of a four-year-old boy by Palestinian mortar fire.
The escalating bloodshed has seen another 76 Palestinians die in Gaza and wounded nine Israeli civilians, one of them critically, since hostilities resumed on Tuesday after the collapse of truce talks and nine days of calm.
In broad daylight outside Gaza's largest mosque, a day after Israel assassinated three of the movement's senior commanders, Hamas gunmen grabbed six men as worshippers came out onto the street after Friday prayers, witnesses told AFP.
They were pushed to the ground. One masked man shouted: "This is the final moment of the Zionist enemy collaborators," before the gunmen sprayed them with bullets.
Earlier, another witness saw 11 people shot dead in a square near the remains of Gaza police headquarters, bombed by Israeli warplanes.
An 18th person was shot in front of bystanders in a separate incident.  
The Hamas-linked website Majd said the 11 were killed after they "gave information to the Zionist enemy".
International human rights organisations condemned the executions.
In Israel, the barrage of Palestinian rockets and mortar fire claimed its fourth civilian victim of the six-week war -- four-year-old Daniel Tragerman, who was killed at home after shrapnel pierced the wall in kibbutz Nahal Oz.
He was the first Israeli child killed by Palestinian fire since July 8.
The army said Gaza militants had fired the deadly mortar shell from a site "adjacent to the Jafar Ali Ibn Taleb school in the Zeitoun neighbourhood of Gaza City" which was "currently serving as a shelter operated by UNRWA".
The military liaison to Gaza "conveyed a severe message to UNRWA and the Palestinian Authority emphasizing that this incident illustrates once more Hamas' exploitation of civilian and UN facilities as a human shield," a statement from the army read.
And Netanyahu said "Hamas will pay a heavy price for this attack," his spokesman Ofir Gendelman said on his Twitter account.
The army and Shin Bet internal security would "intensify ops against Hamas", he added.