The attacks took place in the Mata Khan district of Paktika province near the border with Pakistan Tuesday night, the military and residents said.
"The US aircraft bombed several houses in Ebrahim Kariz village and killed around 40 civilians," Haji Mangal, a tribal elder in the area, told Deutsche Presse-Agentur dpa.
"First the military forces bombed the area and then soldiers descended from helicopters," Mangal said, adding that the dead included several women and children.
An Afghan lawmaker from the province said he had spoken with several sources who told him 33 civilians were killed.
"I have information from the area that 33 people - including women, children, schoolteachers, school students - were killed in the air raid," said Khalid Farouqi, member of the Afghan parliament.
Farouqi said government sources told him eight of the dead were Taliban militants but added, "I have accurate information from the area that all of them are civilians."
Interior Ministry spokesman Zemarai Bashary confirmed the attack and said 31 people were killed in the ground and air operation with most of them being militants, including foreign fighters.
However, the US military said its forces killed several Taliban militants and detained 12 others during the overnight operation in Mata Khan.
The operation also left four civilians - three women and a child -dead while another civilian was wounded, the US military said in a statement.
It said the operation, in which ground forces and airstrikes were used, targeted two militant leaders, who were involved in roadside attacks and foreign fighter operations.
The statement said civilians were killed after the militants attacked US-led coalition forces from inside compounds and a barricaded room.
Because of the remoteness of the area, it was difficult to verify the exact death tolls of insurgents and civilians.
Civilian casualties have become a sensitive issue for the Western-backed Afghan government as many officials have warned that the mounting civilian toll would erode public support for the central government.
More than 1,500 people - mostly insurgents and civilians - have been killed in fighting in Afghanistan so far this year while a quarter of the about 8,000 people who died in violence last year were also noncombatants. dpa fp tl ls
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