Iran says it has detained several "spies" it claims were behind cyber attacks on its nuclear program.

The intelligence minister, Heydar Moslehi, said western "spy services" were behind the complex computer virus that recently infected more than 30,000 computers in industrial sites, including those in the Bushehr nuclear power plant, appearing to confirm the suspicion of computer security experts that a foreign state was responsible.

The announcement also suggests that the attack involving the Stuxnet worm virus, which computer experts believe may have been designed to spy on Iran's nuclear facilities rather than destroy them, has caused more alarm in the regime than has so far been acknowledged.

In remarks carried on Iranian state television and the Mehr news service, Moslehi said Iran had discovered the "destructive activities of the arrogance [of the west] in cyberspace", adding that "different ways to confront them have been designed and implemented".

"I assure all citizens that the intelligence apparatus currently has complete supervision on cyberspace and will not allow any leak or destruction of our country's nuclear activities."

Moslehi gave no details of when the arrests had taken place or whether those detained were Iranians or foreign citizens.

According to experts the Stuxnet worm, designed to be delivered through a removable drive like a USB stick, is one of the most complex pieces of malicious code ever deployed. It was written specifically to attack Siemens industrial control units of the kind used in the Iranian nuclear program.

Suspicion for responsibility for the attack has inevitably focused on Israel and the US, although there is little evidence to support this.

The announcement of the arrests, intended to reassure Iranians, follows comments last week by another senior Iranian official, Mahmoud Liaii, who said: "An electronic war has been launched against Iran".

Iran has denied that the worm damaged the main control systems at Bushehr, rather infecting the laptops of some workers at the plant. However, the disclosure of the attack coincided with an announcement that the plant's inauguration has been delayed until at least next year because of continuing technical problems.

It was confirmed earlier this week that Iran will start fueling the Bushehr nuclear reactor with enriched uranium fuel over the next few days, months later than had been originally announced.

The vice-president, Ali Akbar Salehi, maintained the delay had nothing to do with the computer worm and said the plant had not been affected in any way.

"We hope to load the fuel into the Bushehr reactor by early October and the necessary groundwork for this is coming together, God willing, so it [the fuel] will be completely put in place in the heart [of the reactor] by November," he told the semi-official ISNA news agency.

In recent years Iran has announced the arrest of nuclear spies on a periodic basis. Three years ago it announced it had broken up a spy ring that had handed nuclear intelligence to the UK.