Iranian Intelligence Minister Mahmoud Alavi said on Wednesday that four people accused of sabotaging one of the country's sensitive nuclear sites were only thieves, Mehr news agency reported.
"These four people were not saboteurs. They cut the fences and entered the area to collect scrap iron and steel and sell it on the market," Mehr quoted Alavi as saying.
"In fact, they were thieves not nuclear saboteurs," said Alavi, adding they were "villagers who had done this before".
Alavi did not specify at which nuclear site the arrests were made.
Iran's nuclear chief Ali Akbar Salehi said earlier this month that four people suspected of attempting to sabotage one of Iran's nuclear plants were arrested.
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On Wednesday he said: "If the intelligence ministry... says they are thieves, then we accept it, but what an interesting thief who dug under the concrete wall and tried to enter the site."
Tehran is at loggerheads with world powers over its disputed nuclear programme, which the West and Israel suspect is aimed at making a atomic bomb despite the Islamic republic's repeated denials.
In August last year, saboteurs blew up power lines supplying Iran's underground uranium enrichment plant at Fordo outside the central city of Qom.
In 2010, a cyber-attack hit Iran's nuclear facilities. The Stuxnet virus was tailored specifically to target uranium enrichment facilities.
In recent years, Iran has detained a number of alleged US or Israeli agents accused of spying on, or attempting to sabotage, its nuclear programme.
Several Iranian nuclear engineers have also been killed in what Tehran says were assassinations by foreign intelligence services.