Nato said it was examining its rules of engagement in Afghanistan tonight after the "unfortunate" deaths of 25 civilians in an airstrike in a British-controlled region of Helmand province.

Twelve members of the same family were among those reportedly killed last night after Nato forces responded to a Taleban attack in the Girishk district of Helmand. Up to 30 insurgents were also died in the fighting.

The deaths — the latest in a chain of similar incidents — prompted Nato's Secretary General to say that a "serious investigation" would take place into what happened.

"We continually have to look at our procedures and that is what’s happening," Jaap de Hoop Scheffer told a press conference in Quebec City. "We continually have to look at rules of engagement."

Mohammed Hussein Andiwal, the provincial police chief in Helmand, said a total of 25 civilians and 20 Taleban fighters were killed in the attack last night by foreign forces and Afghan troops.

President Hamid Karzai, who has repeatedly criticised the high rate of civilian casualties in Nato and US raids against the Taleban, said the deaths were "difficult for us to accept or understand".

Nato's International Security Assistance Force (Isaf) released a statement saying it carried out the air strike after alliance forces came under attack by insurgents.

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

"However, it must be noted that it was insurgents who initiated this attack, and in choosing to conduct such attacks in this location and at the time, the risk to civilians was probably deliberate."

Nato said its counter attack on Thursday, involving small arms fire and backed by air support, killed most of the 30 insurgents who had occupied a compound.

Mr Andiwal, the local police chief, told Reuters: "Nine women and three children have been killed in one family in the bombardment."

He said that the rest of the civilians were killed when several houses in another part of the small village were also hit.

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