This photo, taken by an individual not employed by the Associated Press and obtained by AP outside Iran, shows two opposition demonstrators flashing victory signs during a protest in Tehran last Friday. The Iranian regime's restrictions on foreign media have made it difficult to obtain or verify images of street protests. (Associated Press)

Iranian riot police arrested a number of pro-reform demonstrators Tuesday in the capital, Tehran, in a fresh round of protests over last month's disputed presidential election, according to media reports quoting witnesses.

Due to the Iranian regime's widespread restrictions on foreign reporters, it is difficult to confirm reports of opposition demonstrations over the re-election of hardline President Mahmoud Ahmadinejad.

But witnesses said police clashed with hundreds of protesters Tuesday afternoon and several arrests were made.

Iran's June 12 election outcome, which handed a 2-to-1 victory to Ahmadinejad, had spurred allegations of vote-rigging and sent tens of thousands of protesters from both sides into the streets.

In the crackdown that followed, at least 20 protesters and seven Basijis were killed and at least 1,000 people were arrested. Police said most have since been released, but security forces have continued to round up dozens of activists, journalists and bloggers.

Supreme Leader Ayatollah Ali Khamenei declared the election results valid after a partial recount, but opposition candidate Mir Hossein Mousavi has refused to abandon his campaign against the validity of the result.

On Monday, former Iranian president Mohammad Khatami, a Mousavi supporter, called for a national referendum on the legitimacy of the ruling government.

Iranian authorities claim the post-election turmoil has been instigated by enemy countries aiming to thwart Ahmadinejad's re-election, and officials say some of those detained have confessed to fomenting unrest.

But Mousavi has called such allegations an insult to the country, while his supporters said the confessions were forced.

With files from The Associated Press