White House press secretary Jay Carney issued a statement saying the Obama administration is "deeply concerned" about the matter.
"The president has been briefed on the independent review of Dover Port Mortuary [in Delaware] and strongly supports the Pentagon's efforts to make needed systemic structural changes so that these types of incidents never happen again," Carney's statement said. "The United States has a solemn obligation to compassionately and professionally care for fallen service members and their families, and those we tragically lost on 9/11."
The remains were from the attack on the Pentagon and the downed airliner in Shanksville, Pa.
The Washington Post reported it was the first time the U.S. Defense Department has said some remains of Sept. 11 victims taken to the Dover Air Force Base mortuary later ended up in a landfill.
A Defense Department review showed "several portions of remains" recovered from the Sept. 11 attacks at the Pentagon and at Shanksville ended up in a landfill.
The review did not say how many human remains from Sept. 11 were sent to the landfill, but said the remains "could not be tested or identified," apparently because they were too small or charred to allow for DNA analysis.
The Post reported in November the Dover mortuary for years had disposed of incinerated portions of remains of troops killed in Iraq and Afghanistan in a Virginia landfill.
The report said the process involved unidentified or unclaimed body parts.
After the Post investigation, the Air Force conceded it had dumped the incinerated partial remains of at least 274 service members in the landfill, at least between 2003 and 2008. The practice ended in 2008.