A former Department of Energy employee has been indicted after attempting to hack agency computers to steal and then sell nuclear secrets to Iran, China and Venezuela, US officials said Friday.

Charles Harvey Eccleston, 62, who also worked at the Nuclear Regulatory Commission, was snared in an FBI sting operation that was launched after he entered a foreign embassy and offered to hand over classified information, according to the affidavit.

Eccleston proposed to undercover FBI agents posing as representatives of the unnamed country to design and send Energy Department employees "spear-phishing" emails that contained malware that could be used to extract classified nuclear information.

Eccleston, who faces up to 50 years in prison over the four charges, offered to provide that sensitive information in return for payment.

He was detained by Philippine authorities in Manila on March 27, 2015 and deported to the US.

"As alleged in the indictment, Eccleston sought to compromise, exploit and damage US government computer systems that contained sensitive nuclear weapon-related information with the intent to allow foreign nations to gain access to that material," said Assistant Attorney General John Carlin.

"When asked what he would do if Country A was not interested in obtaining the US government information Eccleston was offering, Eccleston stated he would go to China, Iran or Venezuela, as he believed these countries would be interested in the information," according to FBI documents seen by AFP.

Eccleston, a US citizen who had been living in Davao City in the Philippines since 2011, was sacked from his job in 2010 "due to performance and conduct issues."