Four staff members were sacked and a fifth was forced to resign from the top secret Los Alamos National Laboratory, the birthplace of the atomic bomb that lies deep in the desert of the western state of New Mexico.

The action comes two months after all classified work at the nuclear installation was stopped after discs containing secret computer data went missing and after an intern was injured in an accident at the plant.

"Four employees were terminated and one will resign in lieu of termination, while other disciplinary action was taken against seven other people," laboratory spokesman Kevin Roark told AFP.

The 12 disciplined were among 23 workers suspended in July following a spate of incidents that cast doubt on the security of the Los Alamos plant and forced many of its operations to come grinding to a halt.

Three of those forced out of Los Alamos were linked either to the disappearance of two classified computer storage discs possibly containing nuclear secrets that were reported missing on July 7.

Theories ranged from innocent misplacement of the disks to nuclear technology theft.

The other two employees were somehow involved in another incident in which a 20-year-old intern hurt her retina while performing an experiment with a spectraphysics laser, Roark said.

Another 10 people were cleared of any wrongdoing by the internal inquiry and will return to work, while one remains suspended on full pay while the investigation continues, Roark said.

Now that the internal inquiry is over, operations are slowly resuming at the plant that employs 12,000 people and are expected to reach normal levels by mid-October, the spokesman said.

Classified work is scheduled to "come back on line very soon and operations will be fully up to speed by October," he said.

But while thing are starting to return to normal, the way removable computer storage discs similar to those that disappeared are handled at Los Alamos has been completely revamped.

The discs reportedly went missing from the part of the facility where weapons in the US nuclear arsenal are tested and designed, but it remains unclear who removed them and what happened to them.

While the plant was virtually idled for two months, officials insisted that the action in no way jeopardized the security of the US nuclear stockpile.

Los Alamos, where the world's first atomic bomb was designed and tested in 1945, has long been dogged by security breaches and allegations of spying, theft and fraud at the installation.

The lab came under intense scrutiny and criticism after Taiwan-born nuclear scientist Wen Ho Lee was accused of stealing nuclear secrets for China after he was arrested and fired in 1999.

Lee, a US national who worked more than 20 years at Los Alamos, was arrested and held for nine months on suspicion of spying, although the government never gathered sufficient evidence to prosecute him.

He was accused of failing to follow rules on handling highly-classified information, but despite the US government's investigation of Lee's contacts with Chinese colleagues, it never filed espionage charges against him.

Lee was released in September 2000 under a plea bargain agreement in which the FBI was forced to drop all but one of the 59 charges brought against him.

And the laboratory's last head, John Browne, and his deputy quit their posts in January 2003 amid charges of rampant theft, fraud and security lapses at the facility.

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