US space agency NASA removed five members of a nine-person panel and two of its consultants after they warned it last year that its shuttles faced safety troubles and urged an increase in the budget to correct the problem.

A sixth member, Admiral Bernard M Kauderer, was so upset at the firings that he quit the group.

The panel is an advisory body comprising group of industry and academic experts charged with monitoring safety at NASA.

Successive administrations reduced NASA budget and as a result several safety concerns were swept under the carpet.

Rather than looking for more, NASA was looking for less, an expert told a television network.

Problems with the tiles that protect the shuttle body from searing heat as it reenters the earth were known for long but ignored, critics say. It is these tiles that are now main focus of inquiry in the Columbia break-up as it was reentering the earth's atmosphere.

The crash killed all seven astronauts on board, including India-born Kalpana Chawla.

Some of the fired experts now say the agency was trying to "suppress" their criticism.

NASA denies they were fired for raising safety concerns and said it changed the charter of the group so that new members, younger and more skilled, could be added.

"It had nothing to do with shooting the messenger," Sonja Alexander, a spokeswoman at NASA headquarters in Washington, said.

The New York Times quoted members of Congress who heard testimony from the panel last spring as saying that they would re-examine whether budget constraints had undermined safety, but several said they doubted it.