Tehran ? Pro-government crowds swarmed outside the battered home of a key Iranian opposition leader Friday after militiamen attacked with firebombs and beat a bodyguard unconscious in a brazen message of intimidation and pinpoint pressure on dissent.

The assault on Mahdi Karroubi’s five-story residence late Thursday — just hours before major state-backed rallies — displayed the growing tactics of trying to isolate and harass top opposition figures after relentless crackdowns appear to have driven protesters from the streets.

The 72-year-old Karroubi, a cleric and former parliament speaker, has been the most public protest leader in recent months — and has paid the price with repeated damage to his car and tense confrontations with backers of the Islamic state. But the latest backlash, described by a pro-reform website, was by far the most aggressive.

Mobs of hard-line militiamen — known as Basij — began breaking down the front door of Karroubi’s residence before being driven back by warning shots from guards, according to the Sahamnews website, which supports Iran’s pro-reform movement.

Karroubi was at home at the time, but was not injured, his son Hossein told The Associated Press.

Media restrictions imposed by Iranian authorities blocked journalists from reaching the site and independently verifying the accounts. A video posted on the Internet by a group backing the opposition showed smashed windows and graffiti on the walls and door panel of the house, located on a tree-lined street in north Tehran.

Hossein Karroubi said dozens of hard-liners — some on motorbikes — continued to damage the opposition leader’s home on Friday and that police were not responding to the scene. Some security cameras outside the building were torn down, he said.

“The reason for attacking my father is the challenge he raised against the centers of power,” another son, Taghi Karroubi, told the AP. “The attack was very harsh and we feared they wanted to kill (my father).”

The melee came after nearly a week of pro-government gatherings outside Karroubi’s home. The trigger for the assault apparently was to keep him from attending annual pro-Palestinian rallies on Friday and becoming a draw for opposition protesters. Last year, the event turned into street riots after tens of thousands of counter-protests staged marches claiming massive ballot fraud in the June 2009 re-election of President Mahmoud Ahmadinejad.