Increasingly, journalists are being harassed and threatened for attempting to shed light on dark places, but a more insidious tactic of intimidation is being used.
Staff of the BBC Persian service said that recently, several friends and relatives of employees living in Iran have been arrested, interrogated and detained in a "campaign of intimidation" leading up to the parliamentary elections and amid escalating political tensions between Iran and the United Kingdom.
"For the last few weeks we've been coming under increasing pressure, with more and more vicious and outrageous attacks," said Kasra Naji, Special Correspondent at BBC Persian.
"The last few weeks have been worse. This is a campaign of intimidation."
The detention of a BBC journalists' sister in mid-January is the latest attack, which prompted the BBC to become public about the campaign in a broadcast on 2 February.
Security forces raided the home of a BBC Persian employee's relative in Tehran, confiscated her belongings, and transferred her to solitary confinement in the notorious Evin prison. Hours later, a man claiming to be the relative's interrogator at Evin contacted the BBC employee in London, seeking information about the BBC in return for the family member's freedom.
According to Human Rights Watch, the authorities released the detainee on bail several days ago. It is not known whether the family member has been charged with a criminal offence.
"It is different forms of intimidation for different people," Naji added. He said that he was unable to enter the country to care for his father, who recently died in a Tehran hospital after three months of illness, because of his affiliation with the British news outlet.
"Because the BBC is impartial and independent, we are not tolerated by the government in Iran. There is so much censorship, and we are breaking the rule of censorship on an hourly basis. This is what is making them angry and why they are taking a particularly vicious line."
BBC Persian has been under sustained attack since 2009 after its extensive coverage of the disputed 2009 presidential election, with authorities and pro-government websites repeatedly attacking the BBC and anyone affiliated with it.The network has also been systematically jammed, making it inaccessible to anybody in the country without an illegal satellite.
There has been a wave of arrests against journalists and bloggers in Iran in the run up to the parliamentary elections on March 2. Last September, Iranian security forces arrested six independent film makers for allegedly cooperating with BBC Persian on a documentary.
But because of the unprecedented severity of attacks on relatives and friends of the London-based network's staff, the BBC has decided to become public about the situation in a bid to pressure the Iranian government to end the harassment.
"We've thought long and hard. There are many factors to think about, not least the safety of family members of our colleagues in Tehran," said the BBC's Director General Mark Thompson in a broadcast on Sunday.
"What we have decided to do is to be more public than before in calling for the Iranian authorities to desist from this, in asking governments to put on as much pressure as they can, and to hope the embarrassment of this will get those who are responsible for these actions to think again."
"The courage required to report from some of these countries is immense," he added.
According to a Reuters report there was no immediate comment from Iranian authorities.