Up to 11 children and nine adults were killed by an air strike during a NATO operation targeting Taliban commanders in eastern Afghanistan.
Seven Taliban suspects also were killed and five other women were injured inside the house.
The US-led coalition confirmed that airstrikes were called in by international forces during the Afghan-led operation in a remote area of Kunar province near the Pakistan border.
The coalition said it was aware of reports that civilians were killed, but had no immediate information about their deaths.
The death of Afghan civilians caught in the crossfire of battle has been a major point of contention between international forces and the Afghan government.
President Hamid Karzai has forbidden Afghan troops from calling for air strikes and NATO advises crews not to fire at or bomb populated areas.
The airstrike occurred after a joint US-Afghan force faced hours of heavy gunfire from militants.
The forces had launched an operation targeting a senior Taliban leader late Friday in the Shultan area of Kunar's Shigal district.
The deaths came on the same day that a car bomb killed five Americans, including three US soldiers, a young diplomat and a US Defence Department contractor, in the southern province of Zabul.
Mohammad Zahir Safai, the Shigal district chief, said the woman and the children were killed when the houses collapsed on them.
A spokesman for the NATO-led International Security Assistance Force (ISAF), Captain Luca Carniel, said he was aware of reports of civilian casualties and was assessing the incident.
The remote area is one of the main points of entry for Taliban and other insurgents trying to move across the mountainous border from neighbouring Pakistan.