Israel says it might have 'fired in error' in Hamas killing
Mahmoud al-Adham, 28, was shot by Israeli forces in northern Gaza, a statement from Hamas's armed wing said, claiming him as a member.
It said in a statement it would not let the death go "unpunished" and Israel "would bear the consequences of this criminal act".
In an initial statement, an Israeli army spokesman confirmed forces fired on two "armed suspects approaching the fence in the northern Gaza Strip".
Hamas' armed wing has observation points close to the border fence.
But later in the day, the military signalled it had fired in error.
It said an initial inquiry showed that a Hamas security agent had arrived in the area "because of two Palestinians who were wandering" there.
The army said the initial inquiry showed soldiers misidentified the Hamas agent as "an armed terrorist and fired as a result of this misunderstanding".
"The incident will be reviewed," it said.
At least 295 Palestinians have been killed by Israeli fire in Gaza since major protests began along the border fence in March 2018.
Most were killed during the protests but others were killed by airstrikes or tank fire.
In 2007, Israel imposed a land, sea and air blockade on the strip, effectively turning the coastal enclave into an open-air prison, where basic necessities such as food, fuel and medicines are severely controlled.
Critics say the blockade amounts to collective punishment of the coastal enclave's two million residents.
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