"... Western intelligence sources told The Sunday Times the device exploded when it was 'disturbed' by Iranian troops....
Last week, the country's vice president Fereydoun Abbasi said power lines had been blown up near the facility on August 17 in an attempt to sabotage Iran's "peaceful" nuclear program.
But experts examined the rubble and found a device designed to intercept data from computers at the plant.
The accident signals the loss of an important source of intelligence for the West on Iran's progress towards making a nuclear bomb.
It is not the first time a fake rock has been used for espionage. In 2006 British officials admitted that a fake rock found in Moscow contained spying devices.
And last year a spying system camouflaged to look like a rock was discovered by the Lebanese army near the southern port city of Tyre, which they claimed was put there by Israel.
Meanwhile a prominent Iranian MP, Aladin Borujerdi, has accused German firm Siemens of having sold Iran equipment for its nuclear activities laced with mini-explosives, which were removed, Iranian media reported on Sunday.
Mr Borujerdi, who chairs the parliamentary national security and foreign policy commission, made the allegation in an interview with parliament's ICANA news website (Google translation here).
"Intelligence-security apparatus succeeded in discovering explosives in equipment which were provided to us for our nuclear activities. The explosives were to blow up when activated to disrupt the whole system. Domestic experts nullified the plot of the enemy, however," he was quoted as saying by ICANA.
"The company Siemens, which provided this equipment, must answer for its action," he said...."