The harassment of BBC Persian journalists
For those working for the BBC Persian service, interference and harassment from the Iranian authorities has become a challenging fact of life.
I am hugely proud of how they deal with that relentless pressure, and their unswerving commitment to delivering high quality, impartial journalism.
They arguably have the most difficult jobs in the BBC. They carry them out with unstinting dedication and in the knowledge that their work makes a critical difference to the lives of millions who crave access to free and accurate information, in a part of the world where it is scarce and extremely precious.
In recent months, we have witnessed increased levels of intimidation alongside disturbing new tactics. This includes an attempt to put pressure on those who work for BBC Persian outside Iran, by targeting family members who still live inside the country.
We remain extremely concerned about these actions by the Iranian authorities and the latest case only serves to underline this.
Last week the sister of a BBC Persian member of staff was arrested. She was detained and held in solitary confinement on unspecified charges at Evin Prison in Tehran. Although she has now been released on bail, her treatment was utterly deplorable and we condemn it in the strongest possible terms.
It is just the latest in a campaign of bullying and harrassment by the Iranian authorities, putting pressure on the BBC for the impartial and balanced coverage of events in Iran and the wider region.
It follows the repeated jamming of international TV stations such as BBC Persian TV, preventing the Iranian people from accessing a vital source of free information.
In recent months a number of relatives of members of BBC Persian staff have been detained for short periods of time by the Iranian authorities and urged to get their relatives in London to either stop working for the BBC, or to "co-operate" with Iranian intelligence officials.
In other instances, passports of family members have been confiscated, preventing them from leaving Iran. This has left many BBC Persian staff too afraid to return to the country, even to visit sick or elderly relatives. Some have had their Facebook and email accounts hacked.
In addition, there has been a consistent stream of false and slanderous accusations against BBC Persian staff in the official Iranian media, ranging from allegations of serious sexual assault, drug trafficking, and criminal financial behaviour.
It has also included claims that staff have converted from Islam to Christianity or Baha'ism - potentially a capital offence in Iran as it is considered to be apostasy. This has put our staff, who in most cases left their families behind to come to London and work for the BBC, under immense pressure.
This issue is wider than the BBC - other international media face similar challenges. But it is behaviour that all people who believe in free and independent media should be deeply concerned about.
The BBC calls on the Iranian government to repudiate the actions of its officials.
We also ask governments and international regulatory bodies to put maximum pressure on Iran to desist in this campaign of intimidation, persistent censorship and a disturbing abuse of power.
Mark Thompson is BBC director general.