Washington: Preliminary investigations have revealed that space shuttle Columbia experienced an unusual and sudden rise in temperature in its mid-fuselage minutes before it disintegrated, a top National Aeronautics and Space Administration (NASA) official said.

The temperature in the mid-fuselage rose 32 degrees celsius over the last five minutes of Columbia's flight, Ron Dittemore, who heads NASA's space shuttle programme, said on February 2.

This was followed by an increased sign of drag and the shuttle's computerised flight control system tried to make an adjustment in the flight pattern by bringing the shuttle to the right, Dittemore said.

He said the drag was "indicative" of a possibility of damage or loss of 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 broke off and struck Columbia's left wing as it cleared the launch pad, possibly damaging or dislodging some thermal tiles.

The Columbia disintegrated on February 1 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.

Dittemore said 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 at a press conference 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 Columbia was lost, when the shuttle was flying without rockets or engines at over 20,000 km per hour 207,000 feet above Texas.

Meanwhile, NASA administrator Sean O'Keefe appointed Harold W Gehman, a retired Navy admiral who had earlier led the investigation into the 2000 bombing of the USS Cole, to head an independent team of investigators to probe the Columbia disaster.

Several officials from NASA will join Gehman's team, he said.

O'Keefe said the investigators would examine the incident of the insulation from the fuel tank striking Columbia's left wing during lift-off.

"That's one of the earliest indications. It's one of the areas we're looking at first, early, to make sure that the investigative team is concentrating on that theory," he said.

The manufacturer of the fuel tank said on February 2 that NASA used an older version of the tank, which the space agency began phasing out in 2000. NASA's preflight press information said the shuttle was using one of the newer "super-lightweight" fuel tanks.

Harry Wadsworth, a spokesman for Lockheed, the tank maker, said most shuttle launches use the "super-lightweight" tank and the older version is no longer made. Wadsworth said he did not know if there was a difference in how insulation was installed on the two types of tanks.

O'Keefe said NASA was being careful not to lock onto any one theory too soon. "We are looking at every possible thing," he said on CBS-TV.

With NASA's remaining fleet of three shuttle orbiters grounded for now, the crew of the International Space Station (ISS) will be dependent on Russia's space programme to keep their orbiting home supplied – and possibly for a ride home.

An unmanned Russian cargo ship lifted off successfully from Baikonur Cosmodrome in Kazakhstan on February 2 with supplies for the space station. The crew of the ISS includes two US astronauts and one Russian cosmonaut.

NASA officials said on February 2 that the station has enough food and air to sustain its crew until at least June. A Russian Soyuz spacecraft currently docked in the space station provides a lifeboat for the station's crew if they suddenly need to return to earth.

Another Soyuz, each of which can carry up to three people, was already scheduled to visit the space station with a crew of visiting cosmonauts later this spring.

NASA is concerned about the effect of the shuttle fleet's current grounding on the construction of the multi-billion-dollar ISS, which is already years behind schedule and over budget. Many of the components that still remain to be added to the orbiting laboratory are designed to be delivered to the station in the US space shuttles' giant cargo hold.

PTI