Iranian opposition leader Mir Hossein Mousavi speaks during a campaign gathering in downtown Tehran on June 8. (Vahid Salemi/Associated Press)

Iranian opposition leader Mir Hossein Mousavi announced plans to form a new and inclusive political front on Thursday, while warning his country has become "more militarized" since last month's disputed election.

Mousavi, who has refused to accept the results that acclaimed hardline incumbent President Mahmoud Ahmadinejad the victor of the June 12 vote, said on his website that the new political front would have a charter and legal structure.

He added it would not be a substitute for street protests against the election, which have emerged as one of the greatest challenges to the Iranian regime since the founding of the Islamic Republic in 1979.

Mousavi also implicitly accused the security forces of exceeding their powers under Iran's constitution, suggesting that the "near-coup d'etat atmosphere" was a danger to the Islamic Republic.

Meanwhile, Mousavi's wife said Thursday her 62-year-old brother is among the hundreds arrested in Iran's post-election crackdown.

Police, Revolutionary Guards and the pro-Ahmadinejad volunteer Basij militia arrested more than 2,500 people in their heavy crackdown against protests that erupted in support of Mousavi after the disputed election.

More than 500 remain in prison, including many top politicians from pro-reform political parties, human rights lawyers, journalists and activists.

Arrests have continued in recent weeks, while Tehran has barred most foreign media from working in the country, making it difficult to verify reports of more demonstrations.

Mousavi has demanded another vote and decried the Ahmadinejad government as illegitimate.

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.

With files from The Associated Press