WASHINGTON - A failure by US forces to follow procedures in deadly air strikes in Afghanistan last month "likely" caused the death of at least 26 civilians, the US military said on Friday.

During a May 4 battle with Taliban insurgents in western Afghanistan, US air crews and ground troops acted in accordance with the laws of armed conflict but three air strikes by a B-1 bomber "did not adhere to all of the specific guidance" under US combat rules, a military investigation concluded.

"Not applying all of that guidance likely resulted in civilian casualties," said a summary of the probe released Friday.

The investigation found that about 26 civilians died in the incident but said it was possible that a higher number were killed.

- AFP /ls