Partial remains from some victims of the September 11 attacks were dumped in a landfill, the US defence department has said.
Tuesday's admittance, the first of its kind, comes after a report that exposed years of mishandlings at the US military's major mortuary at the Dover Air Force in Delaware.
The portions of remains that ended up at a landfill came from the 2001 attacks on the Pentagon as well as a hijacked airliner that went down in Shanksville, Pennsylvania, on 9/11, according to the report by an independent panel.
The report also said that remains of some US troops killed in Iraq and Afghanistan had been mishandled at the mortuary.
The military had acknowledged last year that some portions of remains of fallen soldiers had been incinerated and sent to a Virginia landfill, a practice that angered military families and led to a new policy.
Since 2008, the military decided to dispose of unidentified cremated remains at sea.
But the review, released on Tuesday, said "several portions of remains from the Pentagon attack and the Shanksville, Pennsylvania, crash site" were also taken to an unidentified landfill.
"These cremated portions were then placed in sealed containers that were provided to a biomedical waste disposal contractor," it said.
The report contradicts a 2011 US Air Force account which said there were no records that showed how remains at Dover were handled before 2003.
Details of how the 9/11 remains were disposed of were buried as background material in the report, which focused on how to fix management problems at the troubled mortuary.
John Abizaid, the retired general who led the review, told reporters it was unclear how many partial remains of September 11 victims were involved because air force records did not go back as far as the attacks.
"I don't know that there's a way to find out," he said. "This is anecdotal evidence that was told to us by the people that we interviewed."
Michael Donley, the air force secretary, reiterated that the US military had expressed regret over how some remains of 9/11 victims and others had been mishandled.
"We certainly have expressed our regret for the additional grief caused to families of loved ones whose remains were handled in - perhaps a less than ideal or, by some measures, even an inappropriate standard, prior to 2008," said Donley.
The review also contained other revelations of botched management at Dover, with officials raising concerns about problems at the mortuary as early as 2002.
A May 2002 memo referred to worrisome "tracking problems" with remains.
A 2005 investigation confirmed "human remains were misrouted in a fashion constituting dereliction of duty," according to the report.
In 2006, the remains of victims killed in the crash of a naval training T-29 aircraft were disposed of as "medical waste" instead of in a group burial, it said.
The air force in 2008 paid a $25,000 settlement to the wife of a US soldier for "mental anguish and medical costs" due to the loss of his personal effects.
The air force had accepted "responsibility and culpability" over the mismanagement of the Dover mortuary but was now working to ensure no more mistakes occur, Donley said.
"Our focus is from here forward," he said. "We have acknowledged our culpability and responsibility for the lapses in performance over the past several years."
Whistleblowers working at the mortuary raised alarm bells, resulting in an investigation last year that found "gross mismanagement" at the facility, with body parts lost in two cases and remains of others mishandled.
The review issued on Tuesday called for bolstering oversight, restructuring the chain of command overseeing the mortuary and expanding training for staff.
"We think the recommendations we made will strengthen the chain of command and will give it the oversight that's necessary," said Abizaid.
"There weren't proper memorandums of organisational understanding between the various organisations. The chain of command was really not a chain of command."