The head of the Los Alamos National Laboratory has resigned, following allegations of theft and fraud at the laboratory where the first atomic bomb was developed.

It is crucial that we restore public confidence in the management of the laboratory Spencer Abraham US energy secretary

John Browne, a physicist who became the laboratory's director in 1997, will step down on Monday.

The Federal Bureau of Investigation and the Department of Energy are looking into allegedly questionable purchases and the disappearance of computers and other equipment from the complex in the state of New Mexico.

A spokesman for the University of California - which runs the laboratory - said the resignation was a "mutual decision" by Mr Browne and the university, but gave no further details.

"It is crucial that we restore public confidence in the management of the laboratory," Energy Secretary Spencer Abraham said on Thursday.

'Cover up'

The laboratory's management came under fire in November, when two security workers were sacked.

Prosecutors bungled Wen Ho Lee's case

They then alleged that they had uncovered evidence of theft and losses amounting to several million dollars.

The FBI and the Department of Energy looked into the allegations. A number of congressional committees threatened their own investigations.

Commenting on Mr Browne's resignation, one of the dismissed workers told The Associated Press news agency:

"They continue to cover up and to conceal the situation at the lab, and finally they've had to pay for what they've done."

Mr Browne, 62, had no immediate comment.

The laboratory has also been tarnished by security scandals, including missing computer disks and the controversy involving Wen Ho Lee - a Taiwan-born scientist who was jailed for nine months three years ago, after being accused of passing nuclear secrets to China.

He denied any wrongdoing, and pleaded guilty to a single charge after the government's case collapsed.

It was in Los Alamos that scientists developed the first atomic bomb in the early 1940s - under such secrecy that the town did not appear on any maps at the time.