Three human rights organisations have called on the Iranian authorities to "immediately and unconditionally" release an ailing Kurdish journalist and activist whose health conditions "have drastically deteriorated" after staging lengthy hunger strikes.

Mohammad Seddigh Kaboudvand, 50, is currently serving a 10-and-a-half-year prison term in Tehran's Evin prison after being found guilty of "acting against the national security" for establishing the Human Rights Organisation of Kurdistan and proposing a campaign to boycott the 9th presidential election which brought Mahmoud Ahmadinejad to office in 2005.

Amnesty International, the International Federation for Human Rights (FIDH), and its affiliate, the Iranian League for the Defence of Human Rights (LDDHI) said in a joint statement that "the Iranian authorities are responsible for any risks" to Mohammad Seddigh Kaboudvand as a result of his ongoing hunger strike.

Kaboudvand who was named the international journalist of the year at the British Press Awards in 2009, is on hunger strike since May in protest at the Iranian authorities' refusal to grant him permission to visit his sick son. Kaboudvand's son, Pejman, was diagnosed with a rare blood condition and has been "gravely ill" in a Tehran hospital for five months, putting the family under immense emotional and financial pressure.

"Mohammad Sadiq Kabudvand is a prisoner of conscience, held solely for his journalistic and human rights work and the peaceful exercise of his right to freedom of expression. He should never have been arrested in the first place, and must be released immediately and unconditionally so that he is free to be with his family at this distressing time," said Ann Harrison, the deputy director of Amnesty International's Middle East and North Africa Programme.

Her comments were echoed by Karim Lahidji, the vice president of the FIDH and President of the LDDHI who warned that the responsibility for Kaboudvand's health rest on the hands of the Iranian authorities.

"The Iranian authorities are responsible for any possible risks to Mohammad Sadiq Kaboudvand's life as a result of his continuing hunger strike and his deteriorating conditions," he said. "Under the UN Standard Minimum Rules for the Treatment of Prisoners, the Iranian authorities are obliged to take immediate action to provide urgent medical care to Mohammad Sadiq Kaboudvand. They must stop further tormenting a father by denying him the right to visit his ailing son."

In an open letter sent from inside jail in May, Kaboudvand described the reasons behind his hunger strike as: "The Prosecutor and the security apparatuses continue to deny [prison] leave because of their enmity, grudge and malice towards me as a human rights activist; this despite my having served half of my illegal and unjust prison sentence and my son's incurable diseases and acute emergency situation... Therefore, to protest the illegal and inhumane behaviour of these judicial and security officials, I launch an indefinite hunger strike as of 9 PM, Saturday 26 May 2012".

In the latest round of harassment against Kaboudvand's family, activists said that security officials have recently prevented his family's access to the media by disconnecting their house landline and his wife's mobile.

Before being imprisoned, Kaboudvand was the editor of the weekly magazine Payam-e Mardom (Message of the People) and co-founded the Human Rights Organization of Kurdistan with other activists which documented and publicised widespread rights' abuses committed by the government security forces in the Kurdish areas in western Iran.

His commitment to the protection of human rights earned him international recognition from organisations such as New York-based Human Rights Watch.