Gaza City (Palestinian Territories) (AFP) - Ten-year-old Afnan Shuheiber was playing on a Gaza City rooftop with her cousins when she became one of at least 73 children killed by Israeli fire in the Gaza Strip.

The spiralling number of children killed in the latest conflict between Israel and the Palestinian group Hamas in Gaza has raised international concern.

On Saturday, a group of international and Palestinian rights groups and aid agencies urged an immediate ceasefire in Gaza, noting the high number of children killed.

"So far, more children have been killed by Israeli fire than Palestinian militants," said a statement from the groups, including War Child and Defence for Children International.

On Saturday, the UN children's agency, UNICEF, said children made up one third of civilian casualties in the conflict so far.

"From July 8th, until 4:00am on July 19, at least 73 Palestinian children have been reported killed as a result of airstrikes and shelling Israel aerial, naval and ground forces," UNICEF's Catherine Weibel told AFP.

She said the children included 53 boys and 20 girls under the age of 18.

"The youngest was reportedly three months old," she said.

More than half of the children killed are under the age of 12.

Afnan, known as Fulla by her family, was among them, killed on Thursday afternoon along with her cousins, Jihad and Wissam, in Gaza City's Sabra district.

Neighbours said the children were taking advantage of the relative lull in the violence that afternoon, going to the roof to relax after days of being cooped up at home.





- 'Tragic victims' -





At the Shifa hospital, the cousins were lined up side-by-side in front of relatives overwhelmed by grief.

Seven-year-old Wissam's eyes were still open -- he looked to be staring into the distance.

Their deaths came after those of another four children, killed as they played on the beach in Gaza City in strikes witnessed by journalists staying at a beachfront hotel.

Ahed Atef Bakr, aged 10, Zakaria Ahed Bakr, also 10, Mohamed Ramez Bakr, nine, and Ismail Mohamed Bakr, 11, were also cousins.

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Relatives said they too had sought to escape the stifling confines of their homes in Shati refugee camp.

Two strikes hit the areas where they were playing.

The first scattered the crowd of adults and children who were next to straw beach huts.

A second followed as they ran along the sand in fear.

The Israeli army later said that a preliminary investigation showed the children were the "tragic" victims of a strike targeting "Hamas terrorist operatives".

A senior army official said on Saturday that the military was "sorry" about the deaths of women and children.

"When you fight there are mistakes," he said.

Gaza is home to 1.8 million people, one of the most densely populated places on earth.

Israel alleges that Hamas uses the population as a human shield and fires rockets from civilian areas and infrastructure.

Weibel said the number of children among the dead in Gaza was of "deep concern" to UNICEF.

"Children should be protected from the violence, and they should not be the victims of a conflict for which they have no responsibility," she told AFP.





- 'Scarred for life' -





She also raised concerns about the long-term effects of the violence on Gaza's children, many of whom are now living through their third war in less than six years.

Israel and Hamas fought similar conflicts in Gaza in both 2012 and over the New Year in 2009.

"You have children who are going to be scarred for life because of what they are seeing," said Weibel.

Even before the war, some 60,000 children in Gaza were in need of psychosocial support, she said, and the number is expected to soar after this conflict.

The potential for such problems is evident every day in Gaza -- wide-eyed children seeing their relatives and friends buried after shelling.

One boy among the crowd hit by Israeli fire on the beach escaped unhurt, but was hysterical and inconsolable.

"They're dead, they're dead," he cried over and over.