WASHINGTON - The US Air Force was harshly criticized on Thursday after the disclosure that the partial remains of at least 274 American troops had been dumped in a Virginia landfill.

The Air Force first acknowledged the controversial practice last month and said it had abandoned the practice in 2008.

But it only disclosed the extent of the cases following an investigation by the Washington Post.

The Air Force is responsible for dealing respectfully with the remains of fallen US servicemen at Dover Air Force Base, the main entry point for returning American war dead from the conflicts in Iraq and Afghanistan.

A senior Pentagon official, briefing reporters, left open the possibility that there may be even more cases prior to 2003, the furthest back the Air Force said it could conduct research due to changes in record-keeping.

Congressman Rush Holt, from President Barack Obama's Democratic Party, slammed the Air Force's handing of the affair, calling the practice an "obvious desecration."

"I still don't think we're at the bottom of it," Holt told Reuters. "It's not just that they're hiding it from us. I think they're hiding it from themselves."

The incidents involved residual remains of fallen American troops -- often killed in catastrophic explosions -- that were found after families had received the bodies of their loved ones.

The Air Force has said families of the 274 fallen troops had granted the military authorization to deal with any residual remains, but acknowledged they had not been made aware those remains would end up in a landfill after cremation.

In 2008, the Air Force decided to start disposing of such remains at sea.

At the Pentagon, Captain John Kirby rebuffed accusations that the defense department wasn't taking the matter seriously.

"I don't think there is another federal agency in this town -- I don't think there's another institution in the country -- that does understand more than we do about how to properly treat the remains of our fallen troops," Kirby said.

Air Force Chief of Staff General Norton Schwartz has defended the decision not to fire anyone as a result of the practices. But Defense Secretary Leon Panetta has asked the Air Force to take a second look at the punishment meted out over the affair, after the Office of Special Counsel said the disciplinary action so far did not go far enough.

Panetta has also ordered an independent review of Dover mortuary's current practices.