Another dissident Iranian writer and campaigner against censorship has gone missing in Tehran - the third in as many weeks.

Mohammad Jafar Pouyandeh disappeared on Wednesday afternoon after telephoning home to say he would be visiting a publisher's office on his way back from work.

Pam O'Toole: "There are fears of a deliberate, violent campaign"

His family say they are particularly worried about his safety after a fellow writer, Mohammad Mokhtari, who also disappeared last week, was found dead in mysterious circumstances.

Mr Pouyandeh's disappearance will heighten fears among dissident Iranian writers and opposition figures that hardliners in the Iranian establishment may have launched a deliberate and violent campaign against them.

Along with Mohammad Mokhtari, whose body was discovered in a Tehran mortuary on Wednesday, Mr Pouyandeh was among 134 writers, who signed a famous open letter to the Iranian authorities four years ago, demanding freedom of expression and association.

Both were also part of a group recently called before a revolutionary court over moves to reactivate the dormant professional writers' association.

President Khatami: Undermined by conservatives

The court warned the writers that if they did not halt their meetings, they could be tried for anti-state activities.

The American-based Human Rights Watch said Mr Mokhtari appeared to have been strangled.

It said his death appeared to be part of an increasingly sinister pattern of attacks on opposition politicians and writers.

Another dissident writer, Majid Sharif, died in mysterious circumstances two weeks ago.

A fourth author, Piruz Davani, vanished without trace in August, while two prominent opposition politicians were murdered last month.

The rising number of dissident deaths and disappearances come amid an intensifying power struggle between the moderate President Khatami and his conservative opponents.