The Israeli military had no immediate comment.
Palestinians said Israeli tanks fired at least two shells at a group of militants from the Al Aqsa Martyrs' Brigades, affiliated with the mainstream, Fatah movement, in the northern Gaza town of Beit Hanoun.
Israeli forces have maintained a presence near Beit Hanoun for several weeks, trying to prevent Palestinians from firing rockets at a nearby Israeli town.
Four men were seriously wounded in the shelling, doctors said, and the bodies of two Al Aqsa members arrived at Gaza City's Shifa hospital. Security officials said the body of the third was still in the field, and rescue workers could not reach it because Israeli tanks were operating in the area.
Repeated flare-ups of violence have endangered the U.S.-backed "road map" peace plan, launched officially on June 4 by U.S. President George W. Bush at a summit meeting in Jordan with Israeli Prime Minister Ariel Sharon and Palestinian Prime Minister Mahmoud Abbas.