Churches in Azerbaijan are facing increasing challenges as a result of government fears over religious extremism, Release International has warned.

It says there is growing pressure on Christians in the former Soviet republic and that tough new regulations have made it difficult for churches to complete the necessary registration.

The law was changed in 2009 requiring religious organisations to re-register with the authorities. Release says the registration process is "mired in bureaucracy" and that applications are often refused.

Churches without the proper registration are considered illegal by the authorities and exposed to crippling fines.

Release chief executive Paul Robinson said official registration had become the "biggest obstacle" facing churches in Azerbaijan today.

The warning follows a recent fact-finding trip to the country by Release workers, which included meeting local pastors and Christians.

A human rights lawyer who cannot be named for security reasons told Release of one church that has been in Azerbaijan for 150 years and always had the proper registration until 2009.

"Now, after the change to the Religion Law it's almost impossible for them to get registered," he said.

One pastor received a visit to his home from 30 police officers and officials who told him it was illegal to spread the teachings of Jesus in Azerbaijan, despite religious freedom being guaranteed in the constitution.

He claims to have been told he would be spared prison if he stopped his work as a Christian evangelist.

The pastor refused and was taken to court accused of keeping weapons.

He was forced to spend 18 months behind bars, an experience which has led him to decide against marrying and having children.

"If I am imprisoned again, who is going to look after my wife and children?" he explained.

Mr Robinson said the crackdown was connected to government fears over the spread of Islamic fundamentalism from across the border in Iran.

"Azerbaijan is clamping down on all religious organisations – including churches," he said.

Another pastor explained: "They are afraid that if people [become Christians] they would prefer the interests of Russia over those of Azerbaijan, while fundamentalist Muslims would prefer the interests of Iran."

Pastor Iliya Zenchenko, head of the Baptist Union of Azerbaijan said: "At any moment the pastor of a church can be imprisoned."

Another pastor told of how literature and Bibles were confiscated from his unregistered church during a raid by police.

"In the court the same guys said we found this pistol in the kitchen. They sentenced me to a year's imprisonment. It's very hard to be in prison in Azerbaijan. It is very bad that the government puts godly men into prison," he said.

Despite the difficult circumstances, the church in Azerbaijan is growing. Release reports that, while there were only a handful of Azerbaijani evangelical Christians in 1990, there are an estimated 10,000 today.

One Christian said: "Please pray for us – pray for freedom, that believers can come together without being afraid of the Government, the police, security services or extremists.

"Pray that Christians will be able to find work, as many are jobless, and pray too that there will be those who can represent and defend the rights of believers in Azerbaijan."