The Iranian pastor held in prison for six years for Christian activities that Iran brands crimes against the state, has been released, according to charity and advocacy groups.

Behnam Irani, 43, was first arrested in December 2006, four years after he became a pastor.

In April 2010, security forces reportedly raided one of his house church services, assaulted him and took him into custody, while other security officials interrogated those attending the service and confiscated Bibles, Christian literature and DVDs.

The evangelical Christian from Karaj city was sentenced in 2011 to six years in prison for action against the state.

In 2014, it emerged that Irani faced 18 new charges, including one for a capital crime.

"Irani has been released from prison and is now free," advocacy group Present Truth Ministries (PTM) was quoted as saying by BosNewsLife. "We thank you all for your prayers. The Lord has preserved him in a mighty way!"

Separately, partners of Release International (RI) confirmed that Irani had been freed. "However, he is said to be in poor health following his ordeal in Ghezal Hesar prison, reputedly one of the toughest jails in Iran," RI said.

The group's CEO, Paul Robinson, said: "Release International is delighted that Pastor Irani has finally been set free. We have been campaigning for this for years.

"However, our partners report that 200 other prisoners remain in jail in Iran because of their faith – a number have been arrested over the past year. Like Behnam Irani, many of these Christian prisoners have been beaten, abused and threatened.

"Release urges Iran to end its long-running crackdown on the church and set free all of its prisoners who are behind bars for their religious beliefs."

PTM said that Irani "came to know Jesus Christ in 1992 and has been a pastor since 2002."

In 2008, Irani was given a five year suspended sentence. According to BosNewsLife, "Irani continued his activities as an effective evangelical pastor of a 300-strong house church congregation of the evangelical Church of Iran movement, raising anger among authorities in this strict Islamic nation."

PTM said: "Brother Behnam was in prison for two months then he was released on bail in June 2010. In January 2011 he was tried for and convicted of crimes against national security. Basically, in this instance, crimes against national security is holding house church services and leading Muslims to Christ."

Irani gave a rare interview with BosNewsLife from prison, through a mediator, saying: "I've the joy of the Holy Spirit. I'm very thankful for Christian activists who are fighting alongside with us."

The pastor confirmed at the time that he was in poor health – including reported intestinal problems and rheumatism – due to mistreatment and poor hygiene in the prison, but said he is "is fighting".

Irani was expected to be reunited with his family: he is married to Kristina, an Armenian Christian, and has a daughter, Rebecca, 11 and a son Adriel, 5.

Iran has a long history of human rights abuses and persecution of Christians.

Earlier this month, three Iranian Christians were sentenced to 80 lashes for taking communion wine. Like Irani, they face charges of crimes 'against national security'.

It is illegal for a Muslim to drink alcohol in Iran and these Christians are converts from Muslim backgrounds. According to RI, "These charges reflect the state position that once a Muslim, always a Muslim."

Robinson said: "Why should Christians be whipped for taking communion? Release calls on Iran to give its citizens freedom of religion, and to stop confusing that most basic of human freedoms – freedom to choose your faith – with state security."

RI added: "There is a risk the pastor could still be charged with apostasy – converting from Islam – which carries the death sentence."

Christians make up one half of one per cent of Iran's population.

In 2010, Ayatollah Khamenei branded house churches a threat to national security.