Civilian deaths in Nato strikes have soured Afghan feelings towards foreign forces  [EPA]

A NATO air strike has killed at least 14 civilians, including eight children, in the eastern Afghan province of Khost, local police say.

But Nato said four Taliban members had been killed in the strike and that it was investigating reports of civilian casualties.

The deadly air raid came a day after two children were reportedly killed in a separate air strike in southwest Ghazni province.

The killing of civilians by foreign troops is a major source of friction between Afghan President Hamid Karzai and his Western backers, and has soured the feelings of many ordinary Afghans towards foreign forces.

Earlier this year, two NATO helicopters gunned down nine Afghan boys as they collected firewood in a volatile province in northeastern Afghanistan.

The incident prompted a sharp rebuke from Karzai and a rare apology by David Petraeus, the commander of US and NATO forces. US President Barack Obama also expressed "deep regret" over the killings.

As violence has spread across the country, casualties have risen, and the United Nations said May was the deadliest month for civilians since they began keeping records four years earlier.