"The deaths were the result of heavy bombing by US forces and ground attacks by government forces," said Hamdullah Watandoost, a spokesman for the governor. "We have seen 40 to 50 dead bodies."
He said the Taliban fighters were killed on Monday in the Dozi area of Zabul's Dai Chopan district and the guerrillas' main base there had been overrun.
"Our mopping-up operation continues and we have besieged the entire Taliban force who have no way to escape," he said.
Juman Khan, the police chief of Dai Chopan, said warplanes from the US-led forces in Afghanistan had pounded mountain areas where up to 600 Taliban fighters were thought to be holed up after launching attacks on Friday and Saturday.
He said ground forces, which included about 450 Afghans and two dozen Americans, had captured up to 40 suspects though these could include innocent people. He said the government and Americans had not suffered any casualties.
"The rest of Taliban, I think, have fled," he said. "The bombing has just ended because of darkness. As far as I can see, the Taliban have been defeated totally here and we have captured their bases."
Khan described the Taliban force scattered over rugged terrain as one of the biggest concentrations since the group was overthrown in a US-led campaign in late 2001.
He said it included fighters blamed for attacks in Zabul and neighbouring Uruzgan province on Friday and Saturday.
A death toll of 50 would be the biggest single-day setback for a resurgent Taliban movement in more than a year.
There had been no contact with them since Saturday, when five government soldiers were killed in an ambush by a group of guerrillas who lost four men in an ensuing skirmish.
Surge in violence
A death toll of 50 would be the biggest single-day setback for a resurgent Taliban movement in more than a year. In early June, government forces said they killed 40 Taliban fighters in an operation near the Pakistani border.
Khan said the Taliban force was thought to include Mullah Dadullah, one of the Taliban's top commanders accused of ordering the execution of a foreign Red Cross worker this year. However, it was unclear if any senior figures were among those killed.
The operation in Dai Chopan follows a surge in violence in the past two weeks across Afghanistan in which more than 100 people have been killed, many in attacks blamed on the Taliban.
A 12,500-strong US-led force hunting Taliban remnants and their al-Qaida allies blamed for the 11 September 2001 attacks on the United States, has had only limited success and the whereabouts of key leaders of both groups remain unknown.
They include Taliban leader Mullah Omar and al-Qaida's Usama bin Ladin.
Afghan authorities say the Taliban have been operating in increasingly large groups in recent weeks to attack government troops, officials and aid workers.
Taliban officials say the militia is waging a "jihad" against foreign troops and sees government officials and aid workers as legitimate targets.