Human remains believed to be those of the seven astronauts, including India-born Kalpana Chawla, on board the ill-fated American shuttle Columbia have been located in Texas and Louisiana.

The discovery comes even as investigators struggled to establish the cause of the breakup of the spacecraft, which disintegrated minutes before landing.

"I can confirm human remains from the space shuttle Columbia have been found in the debris in Hemphill, about 180 miles from Dallas where a lot of twisted metal from Columbia have been found,' a spokesman of the local police said, but gave no details.

Two young boys were reported to have found a charred human leg on their farm in Sabine county.

A hospital employee on his way to work reported finding of what appeared to be charred torso and thighbone on a rural road.

Body parts believed to be from the astronauts have also been recovered near Hemphill, along with a helmet and uniform badges. The remains have been sent for DNA testing, a BBC television report said.

CNN television earlier showed images of a hearse funeral vehicle in a field in Hemphill with investigators standing nearby.

Sabine county sheriff Tom Maddox said, "Several remains have been found." He, however, did not elaborate.

Along with the remains, an intact mission patch, with the names of the seven Columbia crew members has also been discovered.