Palestinian health official Ashraf al-Kidra said three men were killed. Gaza farmers at the scene say the dead men wore military fatigues.
On Wednesday night, Air Force jets struck a terrorist cell in the central Gaza Strip as its members were preparing to fire a rocket into Israel.
Three Palestinians were killed in the airstrike, just east of the Bureij refugee camp. Israel Radio reported that another Palestinian was seriously wounded.
According to the IDF, the same cell had been involved in previous rocket launches at Israel.
Earlier Wednesday, an ultraconservative Islamic group reported that Hamas security forces had detained 20 of its members in a crackdown on rocket fire from Gaza on southern Israel.
The little-known group — the Mujahadeen Shura Council of Jerusalem — posted word of the sweep on its website.
The crackdown was the first in more than a year on ultraconservative Salafi groups operating in Gaza. Hamas currently is believed to be interested in avoiding a conflict with Israel over rocket fire.
At least five rockets were fired into Israel from the Gaza Strip in the past week. All the rockets landed in unpopulated areas causing no injuries or damage.