LONDON (Reuters) - British broadcaster the BBC said on Monday it was appealing to the United Nations to protect its journalists in Iran after it said persecution and harassment by the Iranian authorities escalated in 2017.

“The BBC is taking the unprecedented step of appealing to the United Nations because our own attempts to persuade the Iranian authorities to end their harassment have been completely ignored,” BBC Director General Tony Hall said in a statement.

“In fact, during the past nine years, the collective punishment of BBC Persian Service journalists and their families has worsened.”

Britain’s foreign secretary Boris Johnson said in December he had raised “the official harassment of journalists working for BBC Persian and their families inside Iran” with his Iranian counterpart Mohammad Javad Zarif when he visited Tehran.

The broadcaster said journalists in London working on BBC Persian, part of the BBC World Service, and their families in Iran had been targeted since the satellite TV station launched in 2009.

The harassment escalated last year when Iranian authorities alleged the service’s work was a crime against Iran’s national security and froze the assets of more than 152 current and former BBC Persian staff, it said.

BBC Persian said at the time that it was another step by Iran’s judiciary to silence impartial journalists.

The BBC said other measures against its journalists included the arbitrary arrest and detention of family members in Iran, the confiscation of passports and travel bans preventing people leaving Iran and the spread of fake and defamatory news targeting individuals especially women journalists.

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

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

The BBC said it was planning a series of events in partnership with the International Federation of Journalists this week during the 37th session of the UN Human Rights Council in Geneva.