A NATO airstrike killed at least 27 civilians in central Afghanistan, the Cabinet said on Monday, the third time a mistaken coalition strike has killed non-combatants since the start of a major offensive aimed at winning over the population.

The top NATO commander, U.S. General Stanley McChrystal, apologised to the Afghan President, said NATO.

The Afghanistan Council of Ministers strongly condemned the airstrike Sunday in Uruzgan province, calling it “unjustifiable.”

It said reports indicated that NATO planes fired at a convoy of three vehicles, killing at least 27 people, including four women and a child, and injuring 12 others. An earlier statement said at least 33 were killed.

It urged NATO to “closely coordinate and exercise maximum care before conducting any military operation” to avoid further civilian casualties. The airstrike was not related to the massive ongoing NATO offensive on the southern Taliban stronghold of Marjah in neighbouring Helmand province. But it could still hurt government and NATO efforts to win support from the local population in their fight against Taliban militants.

NATO confirmed that its planes fired on what it believed was a group of insurgents on their way to attack a joint NATO-Afghan patrol, but later discovered that women and children were hurt. The injured were transported to medical facilities, it said in a statement.

The Afghan government and NATO have launched an investigation.

Interior Ministry spokesman Zemeri Bashary earlier said the airstrike hit three minibuses travelling on a major road near Uruzgan's border with central Day Kundi province. There were 42 people in the vehicles, all civilians, he said.

Mr. Bashary said local investigators had collected 21 bodies and two people were missing. He said he was checking with Cabinet officials to find out why there was a discrepancy in the toll.

The NATO statement did not say how many people died or whether all the occupants of the vehicles were civilians.

“We are extremely saddened by the tragic loss of innocent lives,” General McChrystal said in the statement. “I have made it clear to our forces that we are here to protect the Afghan people and inadvertently killing or injuring civilians undermines their trust and confidence in our mission. We will redouble our effort to regain that trust.”

On Saturday, Afghan President Hamid Karzai admonished NATO troops for not doing enough to protect civilian lives. During a speech at the opening session of the Afghan Parliament, Mr. Karzai called for extra caution on the part of NATO.

“We need to reach the point where there are no civilian casualties,” Mr. Karzai said. “Our effort and our criticism will continue until we reach that goal.”

But mistakes have continued. In the ongoing offensive against the Taliban Marjah, two NATO rockets killed 12 people in one home and others have been caught in the crossfire. At least 16 civilians have been killed so far during the offensive, NATO says, though human rights groups say the number is at least 19.

On Thursday, an airstrike in northern Kunduz province missed targeted insurgents and killed seven policemen.

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