BBC director general Mark Thompson said today that the Tehran authorities were waging a programme of "bullying and harassment" against BBC Persian.
In a blog post, Thompson said that last week the sister of a BBC Persian staff member was detained and held in solitary confinement in Iran. She has since been released.
"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," said Thompson.
"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."
Thompson noted that Iran had repeatedly attempted to jam international TV stations such as BBC Persian in a campaign to "prevent the Iranian people from accessing a vital source of free information".
Diplomatic relations between Britain and Iran have deteriorated in recent months due to tensions over Tehran's disputed nuclear programme.
BBC Persian head Sadegh Saba said that direct actions against the BBC by Iran have "intensified" of late.
"We have witnessed increasing levels of intimidation, as well as attempts to interfere with our independence," she said.
"The Iranian government has detained and summoned a number of people allegedly working for the BBC Persian service. There have also been cases of intimidation, questioning and detention involving relatives of BBC staff."
Sarah Leah Whitson, the Middle East director at Human Rights Watch, said that detaining BBC reporters was part of "a wider campaign to harass Iranian journalists by putting pressure on them and their families".
She added: "It suggests that authorities detained the relative to silence the reporter and the BBC. It also sends a message that the government's long arm of repression can extend well beyond borders."
Thompson said that issue of harassment by Iran was "wider than the BBC" as other international media faced "similar challenges".
He repeated calls for the Iranian government to "repudiate the actions of its officials", and asked the UK Foreign Office and international regulatory bodies to exert pressure on Tehran to end "this campaign of intimidation, persistent censorship and a disturbing abuse of power".
> Iran attacks BBC prophet Muhammad series