Victor Reis, Assistant Secretary of Energy for Defence Programmes, has resigned.

Mr Reis oversaw US nuclear weapons laboratories such as the Los Alamos facility in New Mexico belonging to the Department of Energy.

He is expected to leave his job at the end of July, an Energy Department official confirmed.

Under fire

The Department of Energy is under pressure to tighten security

Reports in Saturday's edition of the Washington Post said Mr Reis was leaving his job because of disagreements with Energy Secretary Bill Richardson about the way to improve security at the laboratories.

Mr Reis was one of several officials who came under fire after a Congressional investigative panel last month accused China of stealing secrets to every key American nuclear warhead made since the 1970s, and passing data to US enemies.

The report drew attention to glaring lapses in US security and counter-intelligence.

Beijing has denied the charges and says they stem from rising anti-China sentiment in the US Congress.

Some Republicans want an agency created within the Department of Energy to oversee security and counterespionage efforts, an approach Mr Reis reportedly supported.

Failing to act

They have accused the Clinton administration of failing to act quickly or firmly enough to halt the leaks once they became apparent.

The charges are likely to be given added weight by reports in Sunday's New York Times that the White House had been told about the stolen nuclear secrets almost a year earlier than it originally admitted.

The White House originally said it had first learned of the possible spying in April 1996, but a number of current and former US officials are reported as telling the Times that the president was informed in July 1995 shortly after US officials first detected it.

Falling short

The Congressional report concluded that the investigation of espionage charges stalled for four years because of what officials called bureaucratic miscommunication, inertia and mishandling.

It said little action had been taken to tighten control on sensitive information, and charged that security at weapons development laboratories still falls short of minimal standards.