In 2009, well-known Iranian journalist Ahmad Zeidabadi was one of dozens of journalists arrested following the re-election of President Mahmoud Ahmadinejad and charged with plotting to overthrow the government with a "soft revolution". He was sentenced to six years in jail, five years of exile and a lifetime ban from practising journalism. In 2011, he has been awarded the UNESCO Guillermo Cano World Press Freedom Prize.

Zeidabadi is former editor-in-chief of the "Azad" newspaper and a contributor to BBC Persian - a particular thorn in the side of Iran's regime.

He was selected by an independent international jury of 12 media professionals, in a tribute to "his exceptional courage, resistance and commitment to freedom of expression," jury president Diana Senghor said.

"Beyond him, also the prize will award the numerous Iranian journalists who are currently jailed," she added. At least 26 other journalists are still behind bars.

Not that jail is new for Zeidabadi. According to UNESCO, he was first arrested in 2000, before being imprisoned again less than a year after his release. But the authorities could not silence him. In 2000, he wrote an open letter from prison protesting the way the courts treat jailed journalists. The letter was widely distributed despite Iran's attempts to suppress it.

According to news reports, Zeidabadi's wife says her husband has been put under severe pressure in prison and has not been granted any leave since his arrest.

The director general of UNESCO, Irina Bokova, who endorsed the jury's decision, also called for his release. "Throughout his career Ahmad Zeidabadi has courageously and unceasingly spoken out for press freedom and freedom of expression.

"Ahead of World Press Freedom Day and in recognition of the concerns expressed by the international jury for his health and well-being, I call on the Iranian authorities to release Mr Zeidabadi from detention."

Last year, Zeidabadi was awarded the Golden Pen of Freedom by the World Association of Newspapers and News Publishers (WAN-IFRA).

The US$25,000 Guillermo Cano award is named in honour of the Colombian journalist who was murdered in front of his office in 1986.