While three Palestinians died in the latest shelling on Friday, a farmer was killed by a shell earlier during the day.
Medics at Kamel Adwan hospital said that the three died when the shelling hit a house.
But some security sources told Al Jazeera that the shell had landed near a house in Beit Lahia and was dragged into the building by three young men, after which it went off and killed them.
The Israeli army said it was checking the report of the shelling.
Five more Palestinians were wounded in the shelling, medics said, adding that the dead men were in their 20s.
Palestinian security sources said none of them were known to be affiliated to armed groups.
Separately, a Palestinian farmer was killed earlier when Israeli artillery shelled the northern Gaza Strip east of the Jabaliya refugee camp.
The victim, Omar Abu Warda, 42, was working in his fields at midday (0900 GMT) when he was struck in the shelling, the sources said. He died in hospital later.
Though Israel dismantled its settlements and withdrew from the Gaza Strip last September, it has retained control of the Palestinian territory's borders, sea and air space.