At least four people were shot dead Wednesday when dozens of Afghan villagers clashed with police over the alleged desecration of the Koran, officials said.
The clashes broke out in Musa Qala, a town troubled by insurgent violence in the southern province of Helmand.
"Four people have been killed and seven others, including two policemen, have been shot and injured in the clash," said provincial spokesman Ahmad Zeerak.
He told AFP it was unclear whether police bullets caused the casualties and said officers had been forced to intervene after "Taliban fighters hiding among the protesters opened fire on police first".
Helmand has been the scene of some of the worst fighting between NATO troops and the Taliban since the 2001 US-led invasion which ousted the militants from power nationally.
Local villagers told AFP that a man in police uniform set fire to copies of the Koran which had been pulled from the shelves of a local mosque.
Local official Mohammad Ismail Hotak said a suspect, who had disguised himself as a police officer, had been detained for questioning.
"We have a suspect in custody who allegedly went to a mosque last night while wearing a police uniform and desecrated the Holy Koran, but our initial information shows he is a member of the Taliban posing as a police," the official said.
Officials denied that any copy of the Koran had been burned.
The Taliban claimed that the suspect was a policeman and vowed revenge for the desecration, a deeply sensitive issue in the extremely conservative Muslim country.
In 2012 US troops set fire to copies of the Koran, sparking days of protests in which about 40 people died.
The incident plunged relations between foreign forces and Kabul to an all-time low and forced US President Barack Obama to apologise.