More than 100 people, nearly half of them Afghan civilians, were killed in Nato air strikes against the Taliban this weekend, an investigation by local officials in Helmand province has concluded.

The civilian deaths are just the latest incident of so-called collateral damage to have occurred in recent weeks - a pattern that even foreign troops admit is rapidly undermining efforts to establish some sort of security in the country and win the support and loyalty of local people.

The assessment of Saturday's pre-dawn air strike in the Gereshk district came from the mayor and police chief, who said that 62 Taliban militants had died during the attacks as well as 45 ordinary Afghans including women, children and the elderly. President Hamid Karzai said this weekend that it was "difficult for us to accept or understand" what had happened .

He has repeatedly called on US, Nato and Taliban forces to do more to prevent civilian casualties, warning that "Afghan life is not cheap and it should not be treated as such". And he has ordered foreign forces to co-ordinate military operations with the Afghan government. "From now on, they have to work the way we ask them to work in here."

Concerns about the impact the fighting is having on civilians, especially children, has been growing since clashes increased after the spring thaws.

Such appeals appear to have had little impact on the operations of Nato's International Security Assistance Force [Isaf] or the US military's Operation Enduring Freedom, both of which are supposed to co-ordinate their actions with the Afghan authorities but often appeared to act unilaterally.

Isaf has previously admitted there was a problem with the number of civilians being killed. But after this latest incident officials disputed the Afghan total. Major John Thomas, an Isaf spokesman told the Associated Press: "We don't mean to trivialise any of those who died but we want to make it clear that we believe the numbers are a dozen or less."

He blamed the Taliban for the civilian deaths, saying: "It's the enemy fighters who willingly fire when civilians are right next to them."

The deaths occurred after fighting late on Friday. Helmand's provincial police chief Mohammad Hussein said Taliban fighters had tried to ambush a joint US-Afghan military convoy and then fled to the village of Hyderabad to take cover.