Human rights activists have told the BBC that officials have raided the home of a lawyer representing Iran's best-known political prisoner.
Ganji was jailed for linking senior officials to the murder of dissidents
His client, journalist Akbar Ganji, is reported to be gravely ill after 48 days on hunger strike.
Mr Ganji was jailed five years ago for linking senior Iranian officials to the murders of prominent intellectuals.
His hunger strike is aimed at achieving his unconditional release. His wife says he is "fighting with death".
Lawyer Abdul Fatah Soltani telephoned a colleague to say officials from the hardline Tehran prosecutor's office had arrived at his home bearing a search warrant.
Mr Soltani was out of the house at the time. The colleague, Mohammad Saifzadeh, says he does not know his current whereabouts.
It is unusual for officials to raid the homes of prominent lawyers in Iran.
But this is an unusual case. Mr Ganji, whose family say has lost more than 25kg (55lb) in weight during his hunger strike, has become a rallying point for reformist politicians, students and human rights activists.
He remains defiant. On Thursday, in an open letter, he called on Iran's powerful Supreme Leader, Ayatollah Ali Khamenei, to step down.
Ayatollah Khamenei, he said, should answer this question - how could this be done in a peaceful way?
There have been calls for Mr Ganji's release from around the world, including from US President George W Bush.
Iran's outgoing President, Mohammad Khatami, has called for him to be given parole.
Iran's hardline judiciary has denied that Mr Ganji is on hunger strike, saying he has been hospitalised for a knee injury and is in good condition.
Officials said his friends were welcome to visit him in hospital.
But a delegation of students and political activists who made a determined effort to do so told the BBC that they were turned away by security officials at the hospital.