The BBC on Friday detailed the latest "escalation" in the "systematic targeting" by Iranian authorities of its Persian Service journalists and their relatives.
In the most recent intimidation, government-affiliated media in Iran published articles and pictures of staff describing them as "a mafia gang" associated with terrorism, BBC TV presenter Rana Rahimpour said at a panel discussion in London.
Iran's judiciary-linked Mizan news agency warned in its report that "God's hand of justice will manifest itself through the arms of the Iranian people and they will be punished for their actions", she said.
"This language is ominous: it has had particular use in the past in reference to extra-judicial killings," Rahimpour noted.
Iran's embassy in London did not respond to a request for comment.
In video testimonies, BBC staff described receiving death threats targeting their children, missing parents' funerals because of travel bans and facing attempts by Iranian agents to recruit them as spies.
Veteran journalist and BBC World Affairs Editor John Simpson, who chaired the event on Friday, said the situation reminded him of the Cold War.
"I hoped we'd never see any more of that disgusting kind of behaviour," he said.
"It's one of the worst things a nation has done to free speech in recent times."
Popularity 'draws fire
The London-based Persian Service -- launched on shortwave radio in 1940 and now also comprising TV and digital output -- says it reaches nearly 23 million people, including around 13 million inside Iran.
But the BBC alleges its journalists and their families have faced worsening persecution and harassment, particularly since a 2009 uprising in the Islamic republic was brutally put down.
Iranian authorities in 2017 launched a criminal investigation of 152 BBC staff and their relatives for "conspiracy against national security", while their assets were frozen -- preventing them from buying or selling property in Iran.
An internal staff survey later that year found 86 of 96 respondents had suffered harassment themselves and 45 had seen their parents interrogated by officials.
"It's the existence of the channel, its popularity, the way that it exists inside Persian living rooms that draws fire," said Tarik Kafala, Controller of BBC World Service Languages.
The British broadcaster does not face intimidation "on this scale" anywhere else in the world, he added.
In recent years it has appealed to United Nations Special Rapporteurs David Kaye and Asma Jahangir and the UN Rights Council in Geneva.
The moves prompted free speech rapporteur Kaye and UN Secretary General Antonio Guterres both to make public calls for Iran's government to stop the harassment.