Iran's Supreme Leader told the opposition today they would face a harsh response if they drew their "swords" against his government.
The warning comes three months after a disputed election that sparked widespread unrest.
The stern comments from Ayatollah Ali Khamenei, delivered at a Friday prayers sermon broadcast live by state media, was a clear signal he would not tolerate any perceived threat to Iran's clerical system of government.
It came at the end of a week in which three senior reformist figures, including allies of opposition leader Mirhossein Mousavi, were detained and the office of pro-reform cleric Mehdi Karoubi was closed, according to reformist websites.
"Resisting the system and taking out the sword against the system will be followed by a harsh response," Ayatollah Khamenei said in his sermon at Tehran University, which was attended by hard-line President Mahmoud Ahmadinejad and top officials.
"If somebody stands against the basis of the (Islamic) system and violates people's security, the system is forced to confront it," he said.
But the Ayatollah, who has final say on all matters of state, added criticism and differences among officials were acceptable.
It was the first time he led Friday prayers since a week after the disputed June poll, when he endorsed Mr Ahmadinejad's re-election and accused Western powers of interfering in Iran's domestic affairs.
The election, which was followed by huge opposition protests, plunged Iran into its deepest internal crisis since the 1979 Islamic revolution. It exposed deepening divisions within its ruling elites and added to tension with the West, already strained over Tehran's nuclear ambitions.
Ayatollah Khamenei did not address the dispute over Iran's nuclear programme, two days after Tehran delivered proposals to world powers involved in efforts to resolve the issue diplomatically.
Mr Mousavi and Mr Karoubi, who finished second and fourth respectively, say the poll was rigged to secure Mr Ahmadinejad's re-election. Officials reject the charge.
The President shored up his position last week when parliament approved most of his new ministers, after almost three months of political turmoil in the major oil exporter.
But reformist leaders, including former President Mohammad Khatami, have made clear they will not give up their struggle, issuing several defiant statements over the last week.
Rights groups say thousands of people, including senior pro-reform figures and Khatami-era government officials, were arrested after the election. More than 200 remain in jail, according to the opposition.
Reuters