A Christian church leader has been set free from prison in Iran but only for a limited time, as nuclear talks enter the final phase between the country and US-led powers.

Pastor Benham Irani has been given release but only temporarily, lasting for 15 days, CBN News wrote.

Irani had to post a $40,000-bond to authorities as a guarantee for his eventual return.

The pastor has been sent to prison twice since April 2010.

A former Muslim, the-now Christian leader has been convicted of committing crimes against Iranian national security.

Pastor Irani is set to go back to prison on July 19 after he gets to visit his wife and children for the first time in over four years.

Last year, Fox News reported that the pastor was given the death sentence for an unusual new charge called "spreading corruption on Earth." He was already behind bars when the new sentence was meted out.

Christian Solidarity Worldwide Chief Executive Mervyn Thomas previously said that his group is "deeply concerned by the new charges against Pastor Irani, "especially the charge of spreading corruption on Earth."

"The charges leveled against Pastor Irani and other Christians are tantamount to an indictment of Christianity itself and mark a renewed escalation in Iran's campaign against Persian Christians under the Rouhani presidency," Thomas said in a statement.

Irani was sentenced to serve six years in jail back in 2011 for his Christian activities, which included leading an evangelical congregation in Karaj, a city less than 15 miles outside the capital. The said congregation had 300 members then.

He was kept in solitary confinement while suffering various health problems, including internal bleeding.

Irani also faced harsh interrogation at the Iranian Ministry of Intelligence and Security upon orders from Iranian President Hasan Rouhani for security forces to undertake a massive crackdown on the Christian community in Iran.

The president and the religious mullahs have seen the conversion of its Muslim population into Christianity as a problem.

"There are a lot of people who are disgruntled with the government and many, for comfort and peace in their lives, are turning to Christianity," said Jason DeMars, founder of Present Truth Ministries. "That's a threat to the regime.

"The more people who turn from Islam, the fewer people they have on their side," DeMars added.