WASHINGTON - US forces failed to follow procedures in carrying out deadly air strikes last month in western Afghanistan that killed dozens of civilians, the Pentagon said.
A military investigation by a senior officer outside Afghanistan found "problems" with US bombing raids in a May 4 battle but it was unclear if the mistakes caused civilian deaths, Defense Department press secretary Geoff Morrell told reporters.
"There were some problems with tactics, techniques and procedures, the way in which close air support was supposed to have been executed in this case," Morrell said.
The Kabul government says 140 civilians died from US air strikes in the western Farah province on May 4 during a clash with Taliban insurgents, making it one of the deadliest such incidents since the US-led invasion in 2001.
The report, details of which were leaked to the media earlier, marked the most direct admission so far from the US military that it had made mistakes in the clash with Taliban forces, which triggered an angry public reaction in Afghanistan.
Civilian casualties -- often from US air power -- have caused growing outrage in Afghanistan and tensions with the Kabul government, with US and Western officials worried about handing propaganda victories to the Taliban.
The investigation found that a B-1 bomber involved in the battle lost contact with its intended target temporarily, Morrell said.
"That plane, because of how it takes its bombing routes, had to break away from positive identification of their target at one point to make its elongated approach," he said.
The finding on the B-1 aircraft was "the fundamental complaint that was rendered I believe from this investigation."
But Morrell said it was unclear if the failure to follow certain procedures resulted in civilian deaths.
"It was just noted as one of the problems associated with these events, not that it was the cause of the civilian casualties," he said.
The investigation was "exhaustive" and it shows "the guys on the ground who are involved in this incident took great pains to limit civilian casualties, to target those who had attacked them," he said.
While Kabul officials put the civilian toll at 140, an earlier probe by the US military in Afghanistan found that 20-30 civilians were killed along with 60-65 insurgents.
And Afghanistan's top rights body has said 97 civilians, most of them children, were believed to have died.
Morrell did not say how many civilians were estimated to have been killed in the air strikes.
He said the latest probe found "the numbers in terms of Taliban killed and civilians who perished in this attack are very similar to those that the Afghan -- some of the Afghan defense officials believe are accurate."
The officer chosen to lead US and NATO forces in Afghanistan, Lieutenant General Stanley McChrystal, warned last week that the war against insurgents could be lost unless civilian casualties were reduced.
McChrystal vowed at a senate hearing that he would examine combat rules and tactics with the goal of preventing civilian casualties.
Defense Secretary Robert Gates has asked McChrystal and the officer nominated as his deputy, Lieutenant General David Rodriguez, to carry out a review of military strategy in Afghanistan and report back in 60 days, Morrell said.
Gates wants the new commander to look at possible changes to military strategy as well as how US forces are deployed at a pivotal moment in the war.
The number of US forces will rise to about 68,000 in Afghanistan by the end of the year, after President Barack Obama approved more than 21,000 additional troops.
Both officers still must be confirmed by the US Senate before taking up their posts in Afghanistan, where US and coalition forces face a growing insurgency challenging the Kabul government in the south and east.
The probe into the May 4 battle, ordered by US Central Command and carried out by Brigadier General Raymond Thomas, reviewed video from aircraft called in to the fight as well as audio recordings of conversations between ground commanders and air crews.
The findings were presented to Gates earlier Monday in an hour-long briefing, Morrell said.
The incident began after insurgents attacked police checkpoints and local police called for help from Afghan and international security forces. Fighting then raged for several hours as US air power was called in.