"About two minutes and 47 seconds give or take (after the launch), we saw three perhaps four pieces come off," said shuttle program manager Wayne Hale, adding that it was unclear whether it was foam or "something else."

"We also saw another piece or two come off at about four minutes 50 seconds," he told reporters at the Kennedy Space Center.

He cautioned, however, that it was "very raw, preliminary data" and would have another report later Tuesday.

But Hale said the debris came off the fuel tank later than officials fear it could damage the shuttle's heat shield.

"Both of those (losses of debris) are interesting because they are after the time we're concern about aerodynamic transport causing damage to the shuttle tiles," he said in Cape Canaveral, Florida.

He did not say that size the debris was.

NASA officials had expected some foam to come off during liftoff, but that it would not be of a size that would endanger the shuttle.

A small piece of foam fell off Discovery's fuel tank a day before the launch, but officials decided the shuttle could fly safely without repairing the gap.

The Columbia shuttle's demise in February 2003 was caused by loose foam that came off during liftoff and pierced its heat shield.

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