Three Iranian Christians have been charged with 'Mofsed-e-filarz', or 'spreading corruption on earth', which carries the death sentence.

Pastor Matthias Haghnejad, Pastor Behmnam Irani and Silas Rabbani have all been charged in recent weeks, Christian Solidarity Worldwide (CSW) reports. All three men are well known and respected leaders within the Church of Iran.

Pastor Haghnejad was originally charged with 'Moharebeh', meaning 'enmity against God' following his arrest on July 5, but has now charged with the more serious crime.

While both crimes carry the death sentence 'Mofsed-e-filarz' is thought to be the more dangerous charge, resulting in more executions.

Pastor Irani has been was given the charge along with 18 new charges against him. In 2011 he was sentenced to six years in prison for his faith. He had been leading a 300-strong evangelical church in Karaj, a city near the capital, Tehran.

Irani is now being held in solitary confinement and is suffering numerous health problems which have been exacerbated by his time in prison.

All three men all being held separately at Ghezal Hesar Prison in Karaj where they have been pressured into confessing they are spies.

Iranian Christians are forbidden from praying in public churches, and converting to Christianity from Islam can carry the death penalty.

"Under international laws, being a religious minority is not a crime, but under certain stipulations in Sharia law they can work their way around that. A lot are converts, and apostasy is a crime, they see that a threat to the Islamic state, and so it becomes a political crime," a spokesperson for CSW said.

American pastor Saeed Abedini is serving an eight-year prison sentence for 'threatening the security of the state', having worked to develop home church communities.

In January, the UN said it was alarmed by the increase in executions under President Hassan Rouhani, who came to power in August 2013. Between January and June there were 411 executions recorded, and eight men have already been executed for 'Moharebeh' this year.

"The new charges are tantamount to an indictment of Christianity itself and CSW is growing increasingly alarmed by what is a clear escalation in Iran's campaign against Persian Christians under the Rouhani presidency and by what is effectively an attempt to gain an apostasy conviction by other means," said CSW chief executive Mervyn Thomas in a statement.