PROTESTERS SET fires and smashed store windows on Sunday in a second day of violence as groups challenging President Mahmoud Ahmadinejad’s re-election tried to keep pressure on authorities.

Anti-riot police lashed back and the regime blocked Internet sites used to rally the pro-reform campaign.

Ahmadinejad dismissed the unrest — the worst in a decade in Tehran — as “not important.” He said Friday’s vote was “real and free”and insisted the results showing his landslide victory werefair and legitimate.

Along Tehran’s Vali Asr street — where activists supporting rival candidate Mir Hossein Mousavi held a huge pre-election rally last week — tens of thousands marched in support of Ahmadinejad,waving Iranian flags and shouting his name.

Mousavi released his first statement since two days of violent protests began, calling on authorities to cancel the election.He said that is the only way to restore public trust.

Mousavi, who has accused authorities of election fraud, urged his supporters to continue their “civil and lawful” opposition to the results and advised police to stop violence against protesters. He has claimed he was the true winner of the election.

The violence spilling from the disputed results has pushed Iran’s Islamic establishment to respond with sweeping measures that include deploying anti-riot squads around the capital and cutting mobile phone messaging and Internet sites used by the Mousavi’s campaign.

There’s little chance that the youth-driven movement could immediately threaten the pillars of power in Iran — the ruling clerics and the vast network of military and intelligence forces at their command — but it raises the possibility that a sustained and growing backlash could complicate Iran’s policies at a pivotal time.

US President Barack Obama has offered to open dialogue after a nearly 30-year diplomatic freeze.

So far, Mousavi has issued mixed signals through his website before it was shut down. He urged for calm but also said he is the legitimate winner of Friday’s election and called on supporters to reject a government of “lies and dictatorship.”