LONDON (Reuters) - The BBC said on Wednesday it had filed an urgent complaint to the United Nations after Iran began a criminal investigation into 152 BBC Persian staff and contributors, accusing them of “conspiracy against national security” in Iran and abroad.

The microphone that newsreader Iain Purdon used to deliver the final BBC World Service news bulletin from BBC Bush House is seen in central London July 12, 2012. REUTERS/Suzanne Plunkett

Iran has frozen the assets of BBC Persian staff, meaning they cannot inherit family assets and preventing them and their families from selling assets, such as property or cars, in Iran.

All individuals on the list work, or have worked, for BBC Persian, part of the BBC World Service. A Reuters correspondent who was working for the BBC until 2015 was also on the list.

“This is the latest in a sustained campaign of harassment and persecution which is designed to pressure journalists against continuing their work for the BBC,” Britain’s publicly funded broadcaster said in a statement.

Tony Hall, Director General of the BBC, added in the statement: “This is not just a campaign against BBC Persian staff but against fundamental human rights, and the BBC calls on the government of Iran to end this legal action immediately.”

Iran accused the BBC of inciting unrest after the disputed re-election of President Mahmoud Ahmadinejad in 2009 and said its journalists were broadcasting against the national interests of the Islamic Republic.

The following year it banned Iranians from contact with dozens of foreign organisations, including the BBC, which it said were seeking to topple the Islamic theocracy.

The corporation said harassment had been going on since Iran’s 2009 presidential election and included staff being attacked in the press and on social media with defamatory allegations.

Many staff had been subjected to fake news accusing them of sexual impropriety or sexual acts which are illegal in Iran, including those which attract the death penalty.

The BBC said it had filed the complaint with David Kaye, UN Special Rapporteur on the promotion and protection of the right to freedom of opinion and expression.

BBC Persian broadcasts news in Persian to Iran and the Persian speaking world from London on TV, radio and online, reaching an estimated audience of 18 million a week.