Human Rights Watch says Iranian authorities are intimidating and arresting relatives and friends of Persian-language journalists working abroad.
The U.S.-based group said security forces raided the home of a relative of a BBC Persian service employee in Tehran in January, and "arbitrarily detained and held him as a hostage for close to two weeks."
HRW said the move "seems to be part of a wider campaign to harass Iranian journalists by putting pressure on their families."
Meanwhile, BBC Director-General Mark Thompson said it was one of several occasions on which employees' relatives have been detained in Iran and "urged to get their relatives in London to either stop working for the BBC, or to 'cooperate' with Iranian intelligence officials."
He said in a blog post that "a campaign of bullying and harassment" against the broadcaster had worsened in recent months.
Compiled from agency and RFE/RL reports