The commander of NATO forces in Afghanistan apologised on Friday for killing civilians, including women and children gathering for a wedding, in an air strike on Wednesday.
President Hamid Karzai says 18 civilians were killed and the air strike had no justification.
NATO previously said coalition and Afghan forces called for an air strike after they came under fire during an operation to capture a Taliban commander in Logar province.
But villagers said there were no Taliban in the two houses that were destroyed.
General John Allen said the incident was being investigated.
Civilian deaths have fuelled resentment against foreign forces and become a rallying cause for the Taliban.