The Afghan president said Thursday that 18 people killed in a NATO airstrike in eastern Afghanistan a day earlier were all civilians.
The deadly incident has further soured relations between NATO and the Afghan government, already outraged by civilian casualties in previous operations.
Wednesday was the deadliest day for civilians in Afghanistan so far this year, with at least 40 people killed, the U.N. said. In the largest attack, a trio of suicide bombers killed 22 people in the busy marketplace of Kandahar city.
NATO has so far said it has no records of civilian deaths from the pre-dawn strike on a house in Logar province. The NATO and Afghan troops were going after a local Taliban leader when the international coalition says they came under fire and called in an airstrike Wednesday.
"This is unacceptable. It cannot be tolerated," President Hamid Karzai said in a statement condemning the strike in Logar. He criticized NATO for not being able to provide an explanation for the vans piled with bodies of women and children that villagers displayed to reporters.
Karzai's office said the president had spoken to a man who was related to some of the victims. He promised a thorough investigation and pledged that those responsible would face justice.
Karzai's condemnation of the strike and NATO's treatment of it served as a reminder of the ongoing tension between Afghanistan and its Western allies. It also came as U.S. Defense Secretary Leon E. Panetta visited Kabul.
NATO confirmed only militant deaths from Wednesday's strike but sent a team to investigate allegations that civilians were killed either along with or instead of insurgents.
Villagers displayed 18 bodies at the provincial capital on Wednesday, including five women, seven children and six men. Afghan officials said then that some or all of the dead men were militants. Since no government officials have visited the site of the attack, it was not clear if there might be additional dead.
Karzai said he was cutting short his trip to China because of the attacks in Logar and Kandahar. He was expected back in Kabul today, said Syamak Herawi, a spokesman for the president.