The BBC's Duncan Hewitt in Beijing: "The scandal continues to rock bilateral relations"

The allegations come in a report released to Congress and the White House. The report says China obtained information about several advanced nuclear warheads, including the miniature version used on the Trident Two missile.

A Chinese foreign ministry spokesman said it was regrettable that the allegations, which China has previously blamed on anti-Beijing politicians, had now been repeated by an official department.

Last month, a Chinese-American scientist was fired from his job at the US Los Alamos nuclear weapons research facility, amid allegations that he had passed information to China.

However, the man, Wen Ho Lee, has not been prosecuted.

The report says that as well as using spies to get the information, China also unearthed it from specialised conferences on nuclear technology and from inadvertent leaks by American scientists.

Damage assessment

The BBC's Washingtron Correspondent, Richard Lister, says is remains unclear how much information has been acquired by China

Mr Clinton: Under fire for policy of engaging China

He says Beijing is also suspected by the Americans of having obtained information about neutron bomb technology.

US intelligence officials say the information gathered by China does not appear to have been incorporated into its weapons stockpile.

But intelligence sources told the BBC the information is expected to be applied within years rather than decades.

Congressional investigation

In February, President Clinton ordered a formal assessment of possible damage to United States security after a congressional investigation into military and commercial links with China concluded that Chinese espionage had harmed US interests.

Republican politicians accuse the Clinton administration of being lax on the issue because it is pursuing a policy of normalising relations with China.

Beijing has always strongly disputed the allegations, saying it has sufficient technical expertise of its own.