TEHRAN - Iranian hardline authorities ordered their opponents on Thursday to cease anti-government protests and denied an opposition website report that troops were heading for Tehran ahead of a planned opposition rally.

The authorities have signalled they will tolerate no more protests after eight people were killed in fiery demonstrations on Sunday during the Shi'ite ritual of Ashura. A nephew of opposition leader Mirhossein Mousavi was killed the same day.

State television showed a group of pro-government demonstrators wearing white shrouds and carrying placards that read: We are ready to sacrifice our lives for the leader -- referring to Supreme Leader Ayatollah Ali Khamenei.

The Jaras opposition website said troops and armoured vehicles were moving towards Tehran and that security forces had deployed in several city squares to foil the opposition rally.

Officials denied the report that troops, which have not previously been used for crowd control, had been called in.

Independent verification was impossible because foreign media have been barred from covering protests directly.

Iran's Intelligence Ministry accused the opposition leaders of links to foreign enemies and anti-revolutionary groups and vowed to confront them with no mercy unless they changed course.

The authorities have often blamed foreign-backed forces for plotting to topple the clerical establishment, which is also locked in a standoff with the West over Iran's nuclear work.

A deadline set by the United States and its allies for Iran to accept a deal designed to calm fears that Tehran's nuclear programme is a cover for bomb-making expires on Thursday.

Iran, which may face tougher international sanctions in 2010, says its atomic work aims only to produce electricity.
Hardline leaders have been calling this week for opposition leaders to be punished for fomenting unrest in Iran, which has been rocked by political turmoil since a disputed June election.

Iran's police chief warned Mousavi supporters on Wednesday to halt their illegal demonstrations or face harsh treatment.

Authorities have arrested at least 20 pro-reform figures, including three senior advisers to Mousavi, his brother-in-law and a sister of Iranian Nobel Peace Prize winner Shirin Ebadi.

Hundreds of thousands of people have turned out for government-organised demonstrations which saw calls for the execution of Mousavi and Mehdi Karoubi, both losing candidates in the election won by hardline President Mahmoud Ahmadinejad.

The poll, which reformist leaders said was rigged, touched off the worst internal crisis in the Islamic Republic's 30-year history. The government denied any fraud in the voting.

Neither side has shown much appetite for compromise in the six months since then and confrontations look set to intensify, amid a rancorous flood of accusations and counter-charges.

On Tuesday, Abbas Vaez-Tabasi, a representative of Khamenei, said opposition leaders were 'mohareb' (enemies of god) fit for execution under Islamic law.

Prosecutor-General Qolamhossein Mohseni-Ejei urged them to repent or face charges of supporting apostates in defiance of God, the state-run newspaper Iran reported.

(Editing by Alistair Lyon)