The statement may fuel speculation that opposition leader Mirhossein Mousavi could face legal action, six months after he lost to President Mahmoud Ahmadinejad in a vote that plunged the Islamic Republic into months of political turmoil.
Hardline supporters of Ahmadinejad have in the past called for Mousavi to be arrested for fuelling post-vote unrest. Some reformist websites this week warned of such a possibility, urging people to take to the streets if that happened.
Tension has increased in Iran since student backers of Mousavi last week clashed in Tehran with security forces armed with batons and tear gas in the largest such anti-government demonstration in months.
Judiciary chief Sadeq Larijani accused opposition leaders of provoking the students, IRNA said. Students form the backbone of the reform movement in Iran.
"We have enough proof about the leaders of this plot against the system," Larijani said. "It is the judiciary's duty to consider such evidences and cases."
Iran's Supreme Leader Ayatollah Ali Khamenei gave a stern warning to the opposition on Sunday, accusing it of violating the law by insulting the memory of the Islamic state's revered founder, Ayatollah Ruhollah Khomeini.
State television has broadcast footage of what it said were opposition supporters tearing up and trampling on a picture of Khomeini, who led the 1979 overthrow of the U.S.-backed Shah, during Dec. 7 protests.
"SHEER LIES"
Declaring that opposition rallies were illegal, Khamenei made clear he would not tolerate any more protests by reformers seeking to revive their challenge to Ahmadinejad.
Iran's top authority effectively sided with hardliners calling for tougher action against the opposition, which has continued to show defiance over a poll it says was rigged in the conservative incumbent's favour.
When the June 12 presidential election returned Ahmadinejad to power by a wide margin, his reformist foes cried foul and hundreds of thousands of Iranians took to the streets in the biggest anti-government demonstrations in the 30-year history of the Islamic Republic.
The vote exposed deepening establishment divisions in the major oil producer, which are showing no signs of narrowing.
The authorities reject opposition charges of vote fraud and have portrayed huge anti-government protests as a foreign-backed bid to undermine the Islamic state.
Larijani said the opposition leaders harmed the image of the clerical establishment by spreading lies. "By spreading sheer lies like post-election detainees being tortured … they helped our foreign enemies to pressure Iran," he said.
Tehran governor Morteza Tamaddon said Mousavi had called on people to attend last week's protests, IRNA reported.
He said former president Akbar Hashemi Rafsanjani, who backed Mousavi in the vote, "later poured gasoline on the fire by inviting every one to come to the scene."
Thousands of Mousavi supporters were detained after the vote, including senior reformers. Most have been freed but over 80 people have received jail terms of up to 15 years and five have been sentenced to death over the post-vote unrest.
(Writing by Parisa Hafezi and Fredrik Dahl; Editing by Diana Abdallah)
