Details of the clash in Zabul's Daychopan district could not be independently verified.
The province borders Pakistan's Baluchistan, which is rife with regional insurgency and where attacks have been blamed on Taliban fighters.
Meanwhile, security forces, acting on intelligence, on Thursday raided a camp where a wanted commander of the Taliban's Haqqani network was believed to be meeting Taliban fighters.
The Afghan defence ministry said 35 fighters were killed in the clash. Six blew themselves up to avoid capture, it said.
The US military said around 30 died.
It is not clear if the wanted commander, named Sangeen, was among the dead.
The network was founded by Jalaluddin Haqqani, an Afghan Soviet resistance commander, but is now believed to be led by his sons, notably Siraj Haqqani, who is said to be one of the Taliban's most powerful leaders.
Siraj Haqqani reportedly claimed responsibility for an attack targeting a five-star hotel in the capital Kabul in January 2008, and the attempted assassination of Hamid Karzai, the Afghan president, at a military parade in Kabul in April 2008.
In another major clash, the US and Afghan forces said they killed 60 fighters last week in the southern province of Helmand, a den of Taliban activity and opium production.
Violence has reached its highest levels in Afghanistan since the US-led overthrow of the Taliban in 2001.
East Afghanistan, which borders Pakistan, is seeing an influx of US troops as part of the extra 21,000 soliders Washington has sent to battle the Taliban.