A U.S. warplane failed to follow all operational rules in a complex battle in Afghanistan last month that killed an estimated 26 civilians and 78 Taliban fighters, the U.S. military concluded in a report released Friday.

The deaths last month raised the stakes in a growing battle for the good will of Afghan civilians, whose allegiance Defense Secretary Robert Gates has said is crucial if the United States is going to win the faltering war in Afghanistan.

"The inability to discern the presence of civilians and assess the potential collateral damage of those strikes is inconsistent with the U.S. government's objective of providing security and safety for the Afghan people," the report prepared by U.S. Central Command said.

Three U.S. airstrikes conducted after dark near the close of the chaotic fight in the western Farah Province probably accounted for the civilian deaths, the report said. It contained only mild criticism of the B-1 bomber crew involved, however, and the nation's top military official has already said there is no reason to punish any U.S. personnel.

The report contains no surprises — U.S. officials had already given rough estimates of the number of deaths — but provides a vivid narrative of a firefight that also killed five Afghan national police officers. Two U.S. personnel and seven Afghan security officers were wounded.

Local Afghan officials have said as many as 140 people were killed.

The report recommends refining the current rules for operations with the potential to kill civilians and ensuring that training matches the rules.

Other recommendations include improving the military's ability to get its side of the story in front of Afghans faster, something commanders say is frustratingly difficult. The U.S. should be "first with the truth," the report said.

The report promised a follow-up in four months on how well new tactical rules are working.

The chairman of the Joint Chiefs of Staff, Admiral Mike Mullen, told a Pentagon news conference Thursday that he has seen nothing in the investigation that would call for disciplinary action against the U.S. forces involved.

Mullen added that the complex, seven-to-eight hour fight, which stretched from daylight to dark, revealed gaps in the chain-of-command and some training shortcomings that military leaders plan to address.

Mullen said he is satisfied that U.S. forces involved in the battle were sufficiently sure of their targets and believed that civilians would not be injured when they fired.

Defense Secretary Robert Gates has said the accidental killing of civilians in Afghanistan has become one of the military's greatest strategic problems in the faltering war.

Gates has also said the thousands of new U.S. troops deploying in Afghanistan can lessen the reliance on airstrikes that sometimes kill civilians and undermine support for the fight against the Taliban.

He has assigned his new general running the Afghan war to find new ways to reduce the number of deaths.