Named as Bilal Amsha, Ghanim Ghanim and Aiman Bagharna by Palestinian security sources, the shootings occurred when 20 Israeli armoured vehicles continued raiding various towns and villages.
The three men, all in their late twenties, are believed to have been members of the al-Aqsa Martyrs Brigades - an offshoot of Palestinian President Yasir Arafat's Fatah movement.
Locals said occupation forces began shooting as soon as they entered the town and made no attempt at making a single arrest.
A medic said one of the victims had been shot at very close range in the head and stomach.
Their deaths bring the number of Palestinians killed in three days to 13 - only half are believed to have been connected to any resistance movement.
The youngest victim was just 13 years old.
A 16-year-old Palestinian teenager was also killed by Israeli troops in Gaza.
A Palestinian paramedic carries
a wounded child to safety
Occupation forces opened fire on stone-throwing youths when the army forced its way back into Bait Lahiya, where they killed seven Palestinians on Wednesday.
Muhammad al-Malfuh was fatally wounded in the neck as
armored vehicles were withdrawing.
Despite the rising death toll, US President George Bush has rejected international condemnation of Israeli Prime Minister Ariel Sharon.
Bush said world leaders owed him a "thank you" on Wednesday for his government's plans for the Gaza Strip and the West Bank.
Diplomatic sources said Bush and Sharon had also settled most of their differences over Israel's barrier in the West Bank, once derided by the US president as "a wall snaking through" Palestinian areas and a threat to peace efforts.