The military’s investigation into a May 4 airstrike that killed dozens of Afghan civilians has concluded that "significant errors" were made by U.S. personnel, according to a published report.

The New York Times said Wednesday that — according to an unnamed senior American military official — the civilian death toll could have been reduced if proper procedures had been followed by both aircrews and troops on the ground.

Varying claims of the number of civilian dead have been made since the airstrike in Afghanistan’s western Farah province. The Afghan government estimated the civilian death toll at 140. The Afghan Independent Human Rights Commission said 97 civilians died in the attack, though a preliminary U.S. report put the number at around 30.

According to the Times, some of the airstrikes called in over the course of the seven-hour battle should have been aborted.

"In several instances where there was a legitimate threat, the choice of how to deal with that threat did not comply with the standing rules of engagement," the Times quoted the military official as saying.

The official was granted anonymity in exchange for sharing "a broad summary of the report’s initial findings," though the investigation is not yet complete, the Times said.

According to the Times, in one instance, a U.S. aircraft was cleared to attack Taliban fighters, "but then had to circle back and did not reconfirm the target before dropping bombs, leaving open the possibility that the militants had fled the site or that civilians had entered the target area in the intervening few minutes."

In another of the strikes, the Times reported, aircraft struck a compound where militants were massing for a possible counterattack in violation of rules requiring an imminent threat before putting areas with many civilians at risk.

The Times identified the investigating officer as Brig. Gen. Raymond A. Thomas III. The airstrikes were carried out by three carrier-based Navy F/A-18s and an Air Force B-1 bomber. The U.S. troops on the ground included Marines training Afghan forces and members of a U.S. Special Operations task force.

By late Wednesday, officials at U.S. Forces Afghanistan headquarters in Kabul had not responded to questions about the Times report or the status of the Farah investigation.

In late May, Col. Greg Julian, the top U.S. military spokesman in Afghanistan, told Stars and Stripes that officials were seeking to declassify weapon-sight video and other intelligence that would show blame lies with the Taliban.

Julian, echoed by other American officials in recent weeks, said the Farah attack showcased a new Taliban tactic deliberately designed to create an outcry that would take American airstrikes off the table. U.S. forces have long claimed that enemy fighters use "human shields" to prevent soldiers from returning fire.

But this time, the insurgents actually wanted the Americans to attack so civilians would die, Julian said. The enemy fighters even had plans to kill the civilians themselves if the airstrikes didn’t kill enough, allegedly by using grenades to make it look like bombs killed them, Julian said.

During testimony at his confirmation hearing Tuesday, Lt. Gen. Stanley McChrystal, nominated to be the new U.S commander in Afghanistan, said that airstrikes would continue, as would Special Operations raids, which have also been blamed for many of the deaths. But he also warned that unless the number of civilian casualties was reduced, a U.S. victory would be hard to achieve.

"This is a struggle for the support of the Afghan people. Our willingness to operate in ways that minimize casualties or damage — even when doing so makes our task more difficult — is essential to our credibility," McChrystal said. "I cannot overstate my commitment to the importance of this concept."

The general said he intends to review U.S. and allied operating procedures with an eye to minimizing civilian deaths. He also said that if he could obtain more intelligence, surveillance and reconnaissance aircraft, it would sharpen the precision of allied attacks, thereby avoiding unwanted casualties.

Protecting the local population is a key tenet in counterinsurgency campaigns to "win hearts and minds" away from insurgents and for the nation’s elected government. Afghan President Hamid Karzai has repeatedly warned that civilian deaths are causing Afghans to side with the Taliban. The Obama administration is pouring more troops into the country to battle the raging insurgency.

"I believe the perception caused by civilian casualties is one of the most dangerous things we face in Afghanistan, particularly with the Afghan people," he said during the testimony. "We’ve got to recognize that that is a way to lose their faith and lose their support, and that would be strategically decisive against us."

The Associated Press contributed to this report.