Many women and children were killed or injured in the attack
The BBC's Alastair Leithead is the first journalist to reach the scene of a US air raid which Afghan authorities say killed about 50 civilians in the east of the country on 6 July. He reports on what he found:
On a hillside high in the mountains of eastern Afghanistan there are three charred clearings where the American bombs struck.
Scattered around are chunks of twisted metal, blood stains and small fragments of sequinned and brightly decorated clothes - the material Afghan brides wear on their wedding day.
After hours of driving to the village deep in the bandit country of Nangarhar's mountains we heard time and again the terrible account of that awful day.
What began as celebration ended with maybe 52 people dead, most of them women and children, and others badly injured.
The US forces said they targeted insurgents in a strike. But from what I saw with my own eyes and heard from the many mourners, no militants were among the dead.
A big double wedding was taking place between two families, with each exchanging a bride and a groom.
So Lal Zareen's son and daughter were both getting married on the same day.
He gave the account with his son, a 13-year-old groom, sitting at his feet.
"This is all the family I now have left," he said in a disturbingly matter of fact sort of way.
From his story and from those of other survivors, it appears the wedding group was crossing a narrow pass in the mountains which divides the valleys where the two families live.
From nowhere a fast jet flew low and dropped a bomb right on top of the pass near a group of children who had impatiently rushed ahead and were resting, waiting for the women to catch up.
Lal Zareen was waiting expectantly for the guests to arrive when he heard the explosion and began to climb up the steep mountain track to the pass.
Shah Zareen was part of the group up on the path - he had narrowly escaped being caught in the first bomb and told the women to stay where they were as he rushed to help the children.
Shah Zareen picked up one of the injured, ran down to the village and on his way was calling his local member of parliament on a mobile phone to say they had been attacked.
The mourning groom Shah Zareen (L) and his father described the day
But then he heard the second blast - the bomb had been dropped on top of the women and almost all of them had been killed.
Three girls escaped, among them the bride, but as they ran down the hillside a third bomb landed on top of them.
Shah Zareen explained to me how one of the many new graves contained just body parts of two or three people and the graves that had been dug and not filled were for those still missing - once their remains had been found.
The BBC team I was with were the first outsiders to see where the bombs hit - even the Afghan investigators did not climb up the steep mountainside - and there was much evidence to support the story.
The fact we could travel to the area in local cars was proof that Taleban insurgents, al-Qaeda operatives or foreign fighters were not present in the valley.
The local people said they had not seen militants, but admitted there could have been people crossing the high pass as the next ridge along leads to Tora Bora, the notorious insurgent area.
The US military says it is investigating the incident and it is understood they may have some aerial footage from hours earlier showing insurgents moving nearby.
President Karzai has said that patience is wearing thin with US errors
But it is obvious a huge mistake was made on 6 July. A US statement about the bombing said "any loss of innocent life is tragic".
"I assure you we do not target civilians and that our forces go to great lengths to avoid civilian casualties," said Lt Nathan Perry.
The US no longer insists the dead were insurgents, as it did for two days after the bombing, but it could be some time before the investigation is complete.
Civilian casualties are not new to Nangarhar province - last year a convoy of US Marines was hit by a bomb attack and in the chaos they opened fire in a bazaar killing 19 people.
They were sent home and their officers charged, but a subsequent ruling cleared them of any responsibility for the deaths.
I wonder how many enemies have been created in Nangahar as a result of the latest bloodshed?
Mirwais Yasini, a local MP and the deputy speaker of Afghanistan's lower house, made the point that civilian casualties widen the gap between the people and the government, and the international forces.
As another memorial service took place in the mountains, Lal Zareen told me: "I want President Karzai to make sure the people responsible for this face justice."
That will depend on the US findings and how the Afghan government acts.
These mistakes are incredibly costly in a counter-insurgency campaign which relies on winning people over, not forcing them against the authorities.
I wonder how many enemies have been created in Nangarhar as a result of the latest bloodshed?
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