After being banned from taking to the streets, opposition protesters in Tehran have been chanting anti-government slogans from their rooftops and balconies in the last few days, starting every evening at 2200 local time.
But Human Rights Watch has now complained that members of the Basij militia have been raiding houses to stop the protests.
"Witnesses are telling us that the Basijis are trashing entire streets and even neighbourhoods as well as individual homes trying to stop the nightly rooftop protest chants," said Sarah Leah Whitson, Middle East director, in a statement posted on the group's website.
Videos have also been posted on the internet of the aftermath of the raids, showing damage to satellite dishes.
A man interviewed on the video - which the BBC did not shoot, but which appears to be authentic - said he could not complain to the police because they too were involved in the violence.
Some 17 people are thought to have died in street protests in the past two weeks, and Tehran has imposed severe restrictions on journalists and the internet.
The latest developments come a day after US President Barack Obama praised the bravery of protesters in the face of "outrageous" violence.
President Ahmadinejad hit back at Mr Obama on Saturday, repeating his call not to interfere in Iranian affairs.
He said that if European and American officials believed they could affect the way that Iran's government went about its business, they were wrong.
The Iranian authorities are consistently blaming foreigners for what has happened in Tehran, and have accused Mr Mousavi of being in league with them, the BBC's Jeremy Bowen in Tehran says.
Mr Mousavi has called for an annulment of the 12 June presidential vote because of "election rigging".
Iran's powerful Guardian Council is due to give its final ruling on the election on Sunday, but a spokesman on Friday already insisted there had been no election fraud.
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