A NATO air strike killed four Afghan police and two civilians on Thursday, Afghan officials said.
A spokesman for the US-led NATO force in Kabul told AFP that the military was checking the information.
The attack happened after Taliban insurgents attacked a local police post in eastern Ghazni province before dawn and NATO planes were called in to support the officers under attack.
"The NATO planes went there to assist the police, but the post was bombed and four police were killed. Two civilians present were also killed," Fazul Ahmad Tolwak, chief of Ghazni's Deh Yak district, told AFP.
Ghazni provincial administration spokesman Fazul Sabawoon confirmed the incident and gave a similar account.
The issue of civilian casualties in coalition operations is highly sensitive in Afghanistan, where the United States and its NATO allies have been fighting the Taliban for 11 years.
In the past they have provoked harsh criticism from Afghan President Hamid Karzai, who is due to step down at elections next year, which coincide with the scheduled withdrawal of an estimated 100,000 foreign combat troops.
Last week Afghan officials said four civilians, including a child, were killed in a two-day raid against Taliban insurgents by Afghan and international forces in the province of Logar, south of the capital Kabul.
NATO's International Security Assistance Force said it was also investigating those accusations.
After an air strike killed 10 civilians, mostly women and children, in February, Karzai banned Afghan security forces from calling in NATO air strikes.
However it is unclear whether the ban has been enforced and many operations are jointly run by NATO and Afghan forces.
The strike came a day after Taliban gunmen killed 46 people at a court complex in the western city of Farah in a bid to free insurgents standing trial.
All nine attackers were killed in the assault, which started with a huge car bomb at the entrance to the court and continued for eight hours as security forces hunted down one final surviving assailant.
The brazen attack raised further questions about the Afghans' ability to secure the country as NATO winds down its combat mission in the war-torn country by the end of next year.
The Farah death toll was the highest in Afghanistan from a single attack since a Shiite Muslim shrine was bombed in Kabul in December 2011, killing 80 people.
Karzai condemned the court attack as a "massacre" and said Afghans would "not let such killings of Muslims by the Taliban go unpunished".