TEHRAN - Government supporters rallied across Iran on Friday to protest against an opposition insult to the Islamic Republic's revered founder, with some calling for pro-reform leader Mirhossein Mousavi to be executed.

It was the first time such a call was made during a state-sponsored event and signaled increased pressure on the moderate opposition, which has continued to show defiance over a presidential election in June it says was rigged.

Mousavi, this is our last warning. The sedition leaders should be executed, people chanted at a rally in Tehran.

But there were no reports of the kind of clashes that erupted at previous officially-organized events, when Mousavi supporters also took to the streets in a bid to revive their challenge to hardline President Mahmoud Ahmadinejad.

Reformist websites had urged opposition supporters to stay away from Friday's rallies, which took place under a heavy police presence.

Iran's judiciary earlier this week said it had evidence that senior reformist figures had fomented trouble after the poll six months ago, which triggered huge anti-government street protests, and warned of legal action against them.

The judiciary should confront people who continue this sedition ... with the maximum punishment, Mohammad Hossein Rahimian, a representative of Supreme Leader Ayatollah Ali Khamenei, told the crowd in Tehran, Fars News Agency reported.

Ahmadinejad's disputed re-election plunged Iran into political turmoil and exposed deepening establishment divisions.

Tension increased earlier this month when pro-opposition students clashed with the security forces armed with batons and tear gas in the biggest anti-government protest in months.

KHOMEINI INSULT

The authorities accused the opposition of insulting the memory of late revolutionary leader Ayatollah Ruhollah Khomeini by tearing up his picture during the December 7 demonstrations.

The opposition has denied involvement in the incident and accused the government of planning to use it as a pretext to launch a new crackdown on dissenting voices.

Mousavi should be executed ... Death to Mousavi, shouted demonstrators at the pro-government rally in Tehran.

Similar events were held in other Iranian cities, state television said, showing footage of streets packed with people carrying banners and chanting slogans.

Hardliners have called in the past for Mousavi to be arrested for fuelling widespread unrest after the election.

Officially, Ahmadinejad was returned to power by a wide margin, but his reformist opponents cried foul and hundreds of thousands took to the streets in the biggest anti-government protests in the 30-year history of the Islamic Republic.

The authorities reject opposition charges of poll fraud and have portrayed anti-government protests as a foreign-backed bid to topple the Islamic state's clerical leadership.

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.

At Friday's rally in Tehran, demonstrators pledged allegiance to Khamenei, Iran's highest authority under its system of clerical rule.

We are ready to sacrifice our lives for the leader, they shouted, holding photographs of Khamenei and Khomeini, who led the 1979 Islamic revolution and remains widely revered in Iran two decades after his death.

(Additional reporting by Parisa Hafezi and Ramin Mostafavi; editing by Janet Lawrence)