TEHRAN (AFP) - Security forces deployed across Iran's capital to thwart any opposition protests made arrests on Sunday, the second anniversary of the disputed re-election of President Mahmoud Ahmadinejad, witnesses said. Security forces were deployed on part of Tehran's longest avenue, Vali Asr Street, which bisects the capital from north to south, and in nearby areas, they said. Scores of people were detained, witnesses said, after small groups of people were seen on the avenue and in Vanak Square in apparent response to calls for a demonstration by the opposition. Reformist opposition supporters called on their websites and on Facebook for a silent street march to mark the 2009 presidential election, which saw Ahmadinejad win a second term by a landslide. The major security presence prevented people from forming into large groups, witnesses said, as police blocked pedestrian access to roads leading to the avenue. Plain-clothes agents and anti-riot police carrying paintball guns were also seen patrolling the avenue on motorbikes in a show of force, witnesses added. Ahmadinejad, who is now being challenged by the ruling conservatives in his own camp, defeated opposition leaders Mir Hossein Mousavi and Mehdi Karroubi in the 2009 poll, which they continue to denounce as fraudulent. Their opposition to Ahmadinejad sparked a wave of unrest in the Islamic republic, plunging the regime into one of its worst political crises. The protests left scores dead while thousands, including many close to the opposition as well as journalists, were arrested, with some handed long prison sentences. Mousavi, a former prime minister, and Karroubi, a former reformist parliament speaker, have been under house arrest for the past four months. Their access to the outside world was cut off after they called for a demonstration in February, gathering thousands of people.