Iran's judiciary said on Wednesday it had evidence that opposition leaders had fomented tension in the country after a disputed presidential election in June, Reuters reported according to IRNA news agency.
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.