United Nations human rights experts expressed alarm on Friday at a recent flurry of arrests and harsh sentences inflicted on journalists in Iran, including the Washington Post's Tehran correspondent.
"Convicting individuals for expressing their opinion is absolutely unacceptable," the UN's rights monitor on Iran, Ahmed Shaheed, said in a joint statement with five other UN rights experts.
Since May 22, at least 36 people, including journalists, bloggers, filmmakers and authors, have been arrested, summoned or sentenced in connection with journalistic activity or for expressing their opinions on social media, they said.
Washington Post correspondent Jason Rezaian and a photographer, both dual US-Iranian citizens, were arrested along with their spouses on July 22.
The United States, which has no diplomatic ties with Iran, has called for the journalists to be freed, but Tehran, which does not recognise dual citizenship, has insisted the matter is a domestic issue.
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"These cases exemplify the alarming negative trend taking place in Iran," the UN experts said.
"Individuals and journalists exercising their right to freedom of expression and opinion must be protected, not arrested and prosecuted," they insisted.
The experts also decried the harsh penalties being doled out following trials "riddled with procedural irregularities", with recent sentences ranging from six months to 20 years behind bars.
Iranian author, Arzhang Davoodi, was recently sentenced to death on charges of "Moharebeh", or enmity against God, over comments he had made about an Iranian dissident group, they said.
"The imposition of sentences in conjunction with unfair trials and lack of due process, on charges that do not warrant death or lengthy prison terms, constitutes a dismal violation of international human rights law," the experts said.
"Such extreme convictions are simply intolerable and must be overturned," they added.