The victims included women, children and a cleric as well as 20 suspected Taliban militants, according to Mohammad Hussein Andiwal, the Helmand province police chief.

The air strike - which happened late yesterday - was launched in response to an attack on police posts near the town of Gereshk by militants.

It killed 25 civilians including nine women, three babies and the mullah of a local mosque, Mr Andiwal said.

In a statement, Nato said a compound "assessed to have been occupied by up to 30 insurgent fighters, most of whom were killed in the engagement", had been attacked.

"We are concerned about reports that some civilians may have lost their lives during this attack," Lieutenant Colonel Mike Smith, a Nato spokesman, said.

However, he blamed the deaths on Taliban fighters for sheltering among civilians.

"It was the insurgents who initiated this attack, and in choosing to conduct such attacks in this location and at this time, the risk to civilians was probably deliberate," he added. "It is this irresponsible action that may have led to casualties."

There has been increasing anger among Afghans about the number of civilian deaths that have resulted from international military operations.

According to the Associated Press news agency, the latest deaths - if confirmed - will bring the number of civilians killed in NATO or US-led military operations this year to 177. Among these were seven children who died in a US air strike on Sunday.

A total of 169 civilians have been killed in militant attacks this year, including a recent series of suicide bombings.

Afghanistan's president, Hamid Karzai, has faced public protests over the issue.

In an interview with the BBC yesterday, Mr Karzai criticised the rising toll from foreign troop operations. "This is a suffering that increasingly is becoming difficult for us to accept or understand," he said.

However, the new British ambassador to Kabul this week insisted foreign troops were popular among a civilian population wary of a return to Taliban rule.

"Mistakes have been made. I know that, we all know that, we regret them deeply," Sir Sherard Cowper-Coles told the BBC on Wednesday.

"But the Taliban are responsible for five times as many civilian casualties as the coalition forces here." People's main concern was "not about us staying. It's about us going", he added.

Nato has also acknowledged that some civilians died in a three-day battle with Taliban fighters in the central Uruzgan province.

"Some may have been killed at the hands of the Taliban, some may have been caught in crossfire and some may have died in airstrikes against enemy positions," Lt Col Smith said.