A NATO airstrike in Daykundi province in Afghanistan has left 27 civilians dead.
The Afghan cabinet has condemned the killings as 'unjustifiable'.
It is understood a NATO aircraft mistook the civilians for insurgents in an area between Uruzgan and Daykundi provinces.
Civilian casualties have caused friction between the government and foreign forces, who have launched two big offensives in the past eight months in a bid to turn the tide of a growing Taliban-led insurgency.
Initially the Afghan cabinet reported 33 deaths, but later revised that toll.
The attack comes days after a NATO rocket attack on a house killed at least nine Afghan civilians.
Civilian casualties are a sensitive issue in Afghanistan, where Afghan President Hamid Karzai and his Western backers are trying to win the support of the local population.
Last Thursday, a NATO bombing raid in the northern province of Kunduz killed seven Afghan policemen, according to hospital and government officials.
On 15 February, NATO acknowledged that five civilians were killed and two others wounded in an airstrike in southern Afghanistan.
Mr Karzai used Saturday's opening session of parliament to repeat his call for civilians to be protected as 15,000 Afghan, US and NATO troops press ahead with Operation Mushtarak in Helmand.
