Iran said Saturday it has dismantled several U.S.-backed opposition networks that were gathering information on nuclear scientists and finding ways to circumvent controls on the Internet meant to deprive the opposition of its most crucial tool.

A judiciary statement carried on the official IRNA news agency said the networks were set up by Iranian opposition groups, including the People's Mujahedeen, and that 30 of their members were arrested.

"A number of organized American cyber war networks were dismantled and 30 influential suspects were arrested ... in a series of complicated security operations in the information technology and communications field," IRNA quoted the statement as saying.

The government has repeatedly accused the U.S. and Britain of provoking the unrest that followed June's disputed presidential election — charges both Washington and London have denied.

The statement comes as Washington is pushing for tougher sanctions against Iran over its nuclear program, which the U.S. and other nations fear is aimed at producing weapons. Iran denies such an intention and says its nuclear work is only for peaceful purposes like power generation.

The Iranian statement did not say when the suspects were arrested but it accused the U.S. of using such networks to undermine Iran's ruling system under a policy that it asserted originated in 2006 during George W. Bush's presidency.

"The new intelligence battle known as cyber warfare was made part of the U.S. government's agenda," IRNA quoted the statement as saying.

The statement claimed the U.S. Congress approved a $400 million budget for the covert operation that also involved groups seeking to restore Iran's monarchy.

Iranian authorities have launched a broad clampdown on many Web sites, including blogs, independent news outlets and sites linked to opposition leader Mir Hossein Mousavi, who claims he was deprived of the presidency through fraud in the June election.

With anti-filtering software and the use of Web proxy sites, some Iranians have been able to circumvent those controls to browse YouTube, Facebook, Twitter and Farsi-language news sites that were blocked.

The judiciary statement said the targeted networks were using such software to enable the opposition to access the Web, which it depends upon to organize protests and spread its calls for political and social reform.

"Members of the network, after being identified and arrested, confessed that their proxy anti-filter software ... was employed and unfortunately extensively used for espionage purposes," IRNA quoted the statement as saying.

Iran has also brought many activists and opposition leaders to trial throughout the postelection unrest.

In the most recent case, prominent pro-reform activist Azar Mansouri was convicted of endangering national security and sentenced to three years in prison, her lawyer, Mohammad Reza Faqihi, said on Saturday.

Mansouri is the head of the political bureau of Iran's largest pro-reform party, the Islamic Iran Participation Front. Her lawyer appealed the verdict.

Mousavi, the opposition leader, vowed Thursday that the protest movement will stand firm despite the crackdown.

"We all stand until reaching our goals," Mousavi's Web site, kaleme.com, quoted him as saying.