Tears streaming down her face, the Afghan woman sat in a corner of a room with no roof and broken windows, mourning 19 of her closest and dearest relatives. “They were parts of my heart,” she said.

A wounded Afghan boy is seen on a stretcher after a blast in Asadabad, capital of Kunar province June 9, 2009. A blast near a U.S. troop convoy in Afghanistan killed at least one child and wounded 34 civilians on Tuesday, officials said, but witnesses blamed a U.S. soldier for throwing a grenade into a crowd. REUTERS/Stringer (AFGHANISTAN CONFLICT MILITARY) Six weeks after American warplanes bombed her village in Farah province, on Afghanistan’s remote western border, mistakenly killing dozens of innocent women and children, the terror of the moment when the bombs fell and the ground erupted, turning one mud-walled house after another into rubble, still lives in her mind.

“I lost them all at a glance. Why am I still alive?” the 62-year-old woman asked.

The dead men, women and children, many of them her relatives, now lie in graves. The survivors still wonder why their families were wiped out by American airmen with whom they had no quarrel.

The Americans have paid families $2,000 compensation for each of those killed and $1,000 for each person injured. But the bombing in Farah on May 4, which caused the single highest civilian death toll of any incident this year, remains a significant political issue.

It has weakened Afghans’ support for their government, for the presence of international forces and for the war against the Taliban. It has also raised tensions with President Hamid Karzai, who condemns foreign forces for the rise in civilian casualties, partly to bolster his own support in advance of August’s presidential elections.

A United Nations investigation has found that 828 civilians were killed by Afghan or American-led forces last year, most in airstrikes. Reducing civilian casualties will be a critical task for Stanley McChrystal, the US general who takes command of international forces in Afghanistan tomorrow.

There is concern that 21,000 extra American troops will increase civilian casualties as fighting increases. Violence is already at its highest level since the Americans toppled the Taliban at the end of 2001.

The Americans have investigated the Farah bombing but their preliminary findings provided no real answers beyond admitting that a bomber’s crew had violated procedures.

In such cases there has always been a large discrepancy between estimates of the fatalities by Americans and those made by the UN and other agencies. The Americans rarely admit to making mistakes. In Farah, Afghan officials said that as many as 140 civilians died, but the US military put the civilian toll at no more than 30, along with about 65 insurgents. Other international investigators believe that as many 85 civilians died.

Last year the Americans killed 90 civilians in a bombing raid on Azizabad. An investigation by Dispatches, to be broadcast on Channel 4 tomorrow, will show that the Americans carried out the raid on the basis of faulty intelligence provided by an Afghan to settle a score with a rival. He is now on death row. But the American military has still not admitted the truth.

The Farah airstrikes were more straightforward but no less disastrous. They happened during a day of heavy fighting between Taliban insurgents and Afghan forces supported by American marines. During the fighting several 500lb bombs were dropped.

A lull ensued and villagers say many Taliban fighters withdrew. Many civilians fled, too, but some were still crammed into one compound.

At 8pm a B1 bomber dropped a 2,000lb bomb on the compound, which American commanders suspected of sheltering Taliban but which contained mostly civilians.

The bomber had to make an elongated approach, which meant the target should have been reassessed first. “Either their intelligence was so bad and they believed there were no civilians there, or they made a calculation that killing some civilians allowed them to get rid of Taliban fighters, too,” said Rachel Reid, a Human Rights Watch researcher.

The US air force confirmed that its jets hit a “compound in which enemy personnel had gathered after the fight”.

Haji Issa Khan, a tribal elder, denied American reports that the Taliban were shooting from the roofs. “The Taliban were getting into their cars,” he said. The Americans could see the Taliban cars but they didn’t attack them.”

Instead, they hit the compounds. Scores of old men, women and children had sheltered inside. The result turned a meaningless victory in an obscure part of the country into a spectacular own goal and a human tragedy.

“We told the Americans all these problems are of their own making. They are helping the government but they are helping the Taliban as well with their mistakes,” Khan added.

“Coalition forces are treating the Afghan people like prisoners,” said Zarin Zarin, an MP. “They need stricter rules and have got to work more closely with Afghan forces.”

Afghanistan poses a dilemma: it is not possible to precision-bomb small targets in civilian areas without causing what is euphemistically referred to as “collateral damage”.

Now the Americans know that success depends upon the consent of ordinary Afghan people. As McChrystal arrives, a review is under way to reduce civilian casualties. Emphasis is being placed on the propaganda war, which the Americans realise they have been losing.

The American command in its rhetoric seeks to minimise public outrage over civilian deaths – or at least the false assumption that “foreign” forces are responsible for causing more of them than the Taliban. But the procedures built on their calculation that some civilian casualties are justified will have to be changed if the Americans are to stop damaging their own campaign.

This has already happened in Iraq. President George W Bush’s administration used to sanction up to 30 civilian deaths for each attack on a high-value target, an American source said yesterday. It has since dropped to a single digit.

A spokeswoman for US forces in Afghanistan said yesterday that footage of the Farah battle, recorded by aerial cameras, is due to be released tomorrow. “The videos clearly show Taliban fighters massing in the buildings which were bombed,” she said. “The civilian casualties were caused by the Taliban.”

Lawrence of Arabia, who led the Arab revolt against the Turks in the first world war, wrote that the “ideal” fighting weapon was the knife: “The worst was the airplane.”

There are good arguments for the use of close air support to protect troops on the ground. Coalition forces would have suffered many more casualties without it. But it is a blunt instrument. And so it is that, 90 years on, Lawrence is being proved right in Afghanistan.

Additional reporting: Jerome Starkey, Kabul