Witnesses in the southern city of Rafah reported seeing gunmen killing a man in the middle of the street in what appeared to be the execution of someone suspected of collaborating with Israel.
There was no immediate claim of responsibility from any of Gaza’s armed factions.
Israeli strikes on Gaza killed a teenage boy and a woman on Sunday, medics said, raising the overall death toll to 165.
According to emergency services spokesman Ashraf al-Qudra, one strike on the northern town of Jabaliya struck a house, killing a 14-year-old boy.
Shortly afterwards, another strike killed a woman in the Maghazi refugee camp in central Gaza, he said.
Elsewhere, a man injured in an earlier strike died of his wounds, hiking the toll to 165, Qudra said.
More than 1,000 people have been injured in the Gaza Strip.