The brother of Iranian dissident blogger and internet freedom activist Hossein Ronaghi says he has been on a dry hunger strike since his arrest four days ago.

Hassan Ronaghi, also an activist, said in a tweet on Sunday that his brother contacted the family earlier in the day, adding that he is not feeling well because he has also stopped drinking water and fluids.

He said he asked his brother to end the hunger strike but Hossein Ronaghi responded that he would not do that until he is freed.

Iranian social media users have launched an internet campaign since Saturday, and hashtags #Hossein_Ronaghi (in Persian) and #ReleaseRonaghi in English are currently among the most trending on twitter.

According to his family and friends, security forces have 'abducted' him at around 11:00 AM Wednesday near his house after leaving for work.

Ronaghi's father Reza Ronaghi has said Supreme Leader Ali Khamenei was directly responsible for his son's life, threatening to set himself on fire in public if his son is not freed.

Ronaghi was first arrested, along with his brother Hassan, in the aftermath of the disputed presidential elections in 2009 for issuing proxies that allowed journalists and political activists to circumvent internet censorship. He was also charged with insulting Khamenei in his blog posts.

According to Amnesty International, Ronaghi was badly tortured in prison after his arrest in 2009 and underwent at least four operations to fix his damaged kidney which could not be saved and had to be removed.