Preliminary investigations have revealed that the temperature in the mid-fuselage of the Columbia rose by 32 degrees Celsius over the last five minutes of the flight, Ron Dittemore, who heads the National Aeronautics and Space Administration's space shuttle programme, said on Sunday.

This was followed by an increase in drag and the shuttle's computerised control system tried to adjust the flight by bringing the Columbia to the right, Dittemore said.

He said the drag was 'indicative' of a possibility of damage or loss of the thermal tiles that protect the shuttle from burning up during re-entry into the earth's atmosphere.

During the shuttle's liftoff more than two weeks ago, a piece of insulating foam from the liquid fuel tank had broken off and struck the Columbia's left wing, possibly damaging or dislodging some thermal tiles.

The Columbia disintegrated on Saturday minutes before it was scheduled to land in Florida, killing seven astronauts on board, including India-born Kalpana Chawla.

However, Dittemore cautioned that it was far too early to know exactly what effect the temperature aberrations had on the shuttle or what caused them.

He said that even up to the loss of radio contact with the shuttle, ground controllers did not believe that it was experiencing serious problems and the crew probably did not know what was happening.

"A little bit of drag increase and reaction from flight control is not alarming in any sense... [but] when you piece it together with all the other events that we've talked about, we believe that might be a piece of the puzzle," he said in Houston, Texas.

NASA officials also said they would pay 'close attention' to a series of unusual sensor readings on the left side of the orbiter in the seven minutes before contact with the Columbia was lost.

Meanwhile, NASA administrator Sean O'Keefe appointed Harold W Gehman, a retired navy admiral who had led the investigation into the bombing of the USS Cole, to head an independent team of investigators to probe the Columbia disaster.

Several officials from NASA will join the team, he said.

The Columbia Crash: The Complete Coverage