Nearly two months after a U.S. warplane mistakenly attacked a hospital in northern Afghanistan, officials said Friday it remains unclear how many civilians were killed.

In releasing a two-page summary of an international investigation that was intended to assess civilian casualties from the Oct. 3 attack in Kunduz, NATO said efforts are still under way to reconcile reports that put the death total at either 30 or 31.

A separate U.S. military investigation has been completed to more fully sort out what went wrong and to establish the basis for possible disciplinary action against the U.S. personnel involved. That investigation concluded that the crew of the AC-130 gunship that conducted the attack did not know the target was a hospital, but that a combination of human error, technical failures and other mistakes led to the tragedy.

The U.S. investigation report has not been released publicly, but the top U.S. commander in Afghanistan, Gen. John Campbell, said Wednesday it found that 30 civilians had died. Campbell offered his condolences to the victims of what he called a "tragic but avoidable accident caused primarily by human error."

The international investigation, officially called a Civilian Casualty Assessment Team, or CCAT, said it found credible evidence that 31 civilians had died at the hospital run by Doctors Without Borders, also known by its French initials MSF. The team was led by an American one-star general and was comprised of NATO and Afghan government representatives.

The summary of the CCAT report was released Friday by the top NATO commander in Europe, U.S. Air Force Gen. Philip Breedlove. An accompanying statement from Breedlove's office said the figure of 31 deaths came from "early reporting" by Doctors Without Borders and that the charity's own internal review put the number at 30.

"We are continuing to work with MSF to identify the injured and the families of those killed and reconcile" the death totals reported at various times since the attack, the statement said.

The full report by the NATO-Afghan group, which was obtained by The Associated Press but has not been publicly released, said "it is difficult to reconcile" the casualty figures received by various sources.

"However, the CCAT has determined that there is credible evidence of the death of at least 31 civilians and injuries to a further 26, as a direct result of the airstrike," the report said, adding that it was "unable to determine conclusively" the exact number.

"It is highly likely that other civilians were killed or injured as a result of the airstrike," the report added, "although the details of the number and identity of those killed or injured cannot yet be determined."

When the CCAT investigators visited the hospital compound five days after the bombing, they reported eight bodies remaining at the site, the full report said. "The CCAT was not able to positively identify the individuals nor determine whether they were civilians or INS (insurgents), owing to the condition of the bodies," the report said.

The report also said its investigators found no evidence that Taliban members were killed or injured other than those who may have been patients at the hospital at the time of the attack.