Hamas has executed 18 alleged collaborators in Gaza City 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 since hostilities resumed on Tuesday after the collapse of truce talks and nine days of calm.
European governments are now seeking UN action to find a durable ceasefire after Egyptian diplomacy failed to end the worst fighting in the Israeli-Palestinian conflict since a 2000-2005 second intifada.
Israel has vowed no let-up until it can guarantee the safety of its civilians, and Hamas insists that Israel end an eight-year blockade on the tiny, over-populated Palestinian coastal enclave it controls.
At least 2092 Palestinians have been killed since July 8, of whom the United Nations has identified 70 per cent as civilians, and 68 people have died on the Israeli side, all but four of them soldiers.
In broad daylight on Friday 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 said.
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 - a boy killed at home after shrapnel pierced the wall in a southern community.
Police said the boy was four years old, making him the first Israeli child killed by Palestinian fire since July 8.
"Hamas will pay a heavy price for this attack," Netanyahu's spokesman Ofir Gendelman quoted the premier as saying on his Twitter account.
The army and Shin Bet internal security would "intensify ops against Hamas", he added.
The Palestinian president and Hamas's exiled leader Friday urged the United Nations to draw up a "timetable" for the Israeli occupation of Palestinian territories to end, Qatar state media said.
President Mahmud Abbas and Hamas supremo Khaled Meshaal issued the appeal during talks in Doha, as fighting continues in Gaza, Qatar's state news agency QNA said.
The two Palestinian leaders have been holding talks in Doha since Thursday, but little else has filtered out of their meetings which are hosted by the emir of Qatar, a key backer of Hamas.
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