The parents of a British-Greek journalist detained in Iran appealed for his release today insisting that their son was not a spy.

Iason Athanasiadis, also known as Jason Fowden, was arrested at Imam Khomeini Airport in Tehran at the end of last week on charges of “underground activities”. He had been about to fly out of the country after covering the election and its violent aftermath for The Washington Times.

Mr Fowden is the latest victim of a state-ordered media blackout that has seen dozens of journalists taken into custody and many more expelled.

Iran’s state news agency quoted a Culture Ministry official as saying: “I call on foreign reporters to work within our laws when travelling to Iran for news coverage... because if they act against national security and spy, they will be arrested by security institutions and handed over to the judiciary.”

But Mr Fowden’s Greek mother, Polymnia Athanasiadi, and British father, Georgios Fowden, said in a statement yesterday that their son had “always maintained his integrity as an independent journalist”.

They added: “His work serves no purpose other than the fair and humane coverage of life in the many countries where he has worked."

Mr Fowden has covered Iran since 2004 and has contributed articles and photographs to The Guardian, the Financial Times, the Daily Telegraph, and GlobalPost.

In an article published on The Guardian website on June 16, Mr Fowden described a “city literally divided” as supporters of incumbent president Mahmoud Ahmadinejad and his defeated challenger Mir Hossein Mousavi faced off. His last article, a profile of Mousavi, ran in The Washington Times one day later.

A spokeswoman for the Foreign and Commonwealth Office said that Greek officials were providing consular assistance to Mr Fowden, who was travelling on his Greek passport. "We stand ready to help if needed," the spokeswoman added.

There have been conflicting accounts of how many journalists have been detained in Iran since the protests began. Reporters Without Borders puts the figure at 33. Committee to Protect Journalists said 13 were in custody.

Almost all other foreign journalists have been forced to leave the country, including the BBC’s Tehran correspondent, Jon Leyne, who was accused of supporting the post-election violence.

News of Mr Fowden’s arrest also comes just days after London ordered out two Iranian diplomats in tit-for-tat expulsions with Tehran.

David Miliband, the Foreign Secretary, today criticised the Iranian government’s “profound clampdown” and what he saw as its attempts to stoke conflict between Iran and the West.

He said: “It’s not a crisis between Iran and America, or Iran and Britain, however much the Iranian government wants to suggest that.

“The people on the streets are there because of the crisis of credibility of the election results that were announced.”

Miliband said that Britain would make representations on behalf of Mr Fowden. “I think that the free media in Iran is a very important part of its engagement with the outside world,” he said. “It’s a very backward step if the Iranian government start cutting that off."

Times Recommends

• Should Knox’s trial even have reached the courtroom?
• 'Was it real?' The US bailout nightmare
• Iranian opposition plays the long game