Today is the last Friday of Ramadan when Iranians are encouraged to demonstrate their support for the Palestinian people, on what is called Qods day.
But there are reports of thousands of opposition supporters in the streets of Tehran and at least ten arrests in clashes with police.
The marchers are shouting slogans in support of their unsucessful presidential candidate Mir Hossein Mousavi. It follows a warning from the Revolutionary Guards yesterday that any demonstration would be broken up.
Mousavi, along with rival candidate Mehdi Karoubi and former president Mohammed Khatami joined their supporters in the streets, but all reportedly had to flee angry counter-demonstrators.
Today is the first opportunity the opposition has had since July the ninth to vent its feelings in public.