A Nato air strike in southern Afghanistan killed at least 21 civilians, the Afghan government said today.
Nato forces said its planes fired yesterday on a group of vehicles that it believed contained insurgents who were about to attack its forces, only to discover later that women and children were in the cars.
The Afghan government and Nato have launched an investigation.
Investigators on the ground had recovered 21 bodies and two people were missing, Interior Ministry spokesman Zemeri Bashary said. Fourteen people were wounded, he said.
The strike hit three mini-buses that were driving down a major road in the mountainous province. There were 42 people in the vehicles, all civilians, Mr Bashary said.
Nato said that its forces transported injured people to nearby medical centres.
"We are extremely saddened by the tragic loss of innocent lives," Nato commander General Stanley McChrystal said.
"I have made it clear to our forces that we are here to protect the Afghan people and inadvertently killing or injuring civilians undermines their trust and confidence in our mission. We will redouble our effort to regain that trust."
General McChrystal apologised to President Hamid Karzai for the incident, Nato said.
Nato has gone to great lengths in recent months to reduce civilian casualties as part of a new strategy to focus on protecting the Afghan people to win their loyalty over from the Taliban. Rules for air strikes have been tightened, but mistakes continue to happen.
In the continuing offensive against a Taliban stronghold in Helmand province, south of Uruzgan, two Nato rockets killed 12 civilians and others have been caught in the crossfire.
On Thursday, an air strike in northern Kunduz province missed targeted insurgents and killed seven policemen.
The Afghan cabinet later said that at least 33 civilians were killed in the air strike.
In a statement released today, the Afghanistan Council of Ministers strongly condemned the attack, saying it was "unjustifiable".