Iranians connect a cellphone to an amplifier so protesters can hear defeated Iranian presidential candidate Mirhossein Mousavi address them near the Ghoba mosque in northern Tehran on June 28, 2009. (Reuters)

Iranian President Mahmoud Ahmadinejad defended his country's disputed election as the "most free" in the world on Tuesday, while accusing his domestic opponents of collaborating with Iran's international adversaries.

His speech came on the same day as Iran's three top reformist leaders demanded the country's ruling clerics end the "security state" imposed after the June 12 presidential election and release those detained during post-electoral turmoil.

In his first televised address since the country's supreme leader declared the official results of the vote valid, Ahmadinejad said the contests were clean, fair and marked the start of a "new era."

"It was the most clean and free election in the world," he said, adding that, "no fault was discovered" during the recount.

"This election has doubled the dignity of the Iranian nation," he said.

Ahmadinejad again blamed foreign powers for trying to sabotage the vote and criticized his reformist rivals for repeating remarks of Western countries.

"Unfortunately, some people inside Iran collaborated with them," he said.

"The result of their childish acts of interference in Iran's internal affairs is that the Iranian nation and government will enter the global stage several times more powerful," he said.

Crackdown could lead to 'radicalization': opposition warns

After a meeting late Monday in Tehran, defeated presidential candidates Mir Hossein Mousavi and Mahdi Karroubi, as well as former president Mohammad Khatami, warned that suppressing protest could "radicalize" the opposition movement.

The remarks appeared on Mousavi's official website.

The meeting of the three men — the first of its kind by top leaders in the reform movement — appeared to be part of an attempt to resurrect the opposition after the police crackdown.

Revolutionary Guards and pro-government Basij militia shut down massive protests that sprung up after the election in which police said 20 protesters were killed, hundreds injured and more than 1,000 arrested.

Most of those arrested during the protests have been released, according to police, though dozens of pro-reform politicians and journalists are still being held, and arrests have continued.

Although there have been no major street protests for more than a week, the government closed universities and dormitories ahead of Thursday's anniversary of a 1999 attack by Basij and police on protesting students.

The pro-reform camp maintains Mousavi was the real winner in the election, and accuses Iran's ruling system of rigging results to ensure victory for Ahmadinejad, the incumbent.

Karroubi came last in the official results. Iran's supreme leader Ayatollah Ali Khamenei has publicly sided with Ahmadinejad.

With files from The Associated Press