A Christian convert who has been languishing in an Iranian prison for years now will have to endure three more years of deprivation.

Ebrahim Firouzi was earlier handed a five-year prison sentence by Tehran's Revolutionary Court in 2015 after he was arrested for his faith in July 2013 and falsely convicted of "forming a group in order to disrupt national security," the National Council of Resistance of Iran (NCRI) reported.

Late last month, an appeals court confirmed his prison term, which means that he will not be due for release at the Rajai Shar prison until January 2020, according to Mohabat News. After his release from prison, he will reportedly be exiled to Sarbaz township, one of the most deprived areas in Sistan-Baluchestan province.

Iranian authorities have refused to grant Firouzi permission for temporary medical leave even for a single day, even during the Persian New Year's holiday, sources said.

As a result, the Christian convert's health continues to deteriorate, the sources added.

Prison officials have also reportedly prevented Firouzi from visiting his old and ailing mother who has been suffering from cancer and undergoing medical treatment.

Firouzi was arrested and detained on July 3, 2013 on charges of "propagating material against the Islamic republic, launching and leading deceptive Christian evangelical organisations, connection with anti-Islamic revolution elements abroad, and setting up Christian internet sites."

Firouzi has denied all the charges levelled against him, NCRI said. Moreover, parts of the evidence presented at the appeals court were reportedly the same evidence previously presented in an earlier case filed against him, for which he had already served the prison sentence upon conviction.

Iran ranked eighth on Open Doors USA's World Watch list of top Christian-persecuting countries.

The Christian persecution watchdog states that Iranian authorities consider Christianity as a Western influence and a threat to the Islamic identity of the republic.

Muslims who converted to Christianity make up the largest group of Christians and experience the most persecution, the group says.

Christians face extreme persecution in Iran, including regular crackdowns and jail sentences due to their faith. House churches are not permitted, and Christian converts are beaten and arrested for gathering to worship, according to The Christian Post.