Hundreds of Christians in Iran have been arrested and imprisoned since the beginning of this year.
The crackdown has led to 285 believers in 35 cities being arrested in Iran in the past six months, according to Elam Ministries, an organization that serves Christians in that country.
Many of those Christians have spent weeks and even months in prison, often serving long stretches in solitary confinement. They also have endured interrogations and psychological abuse.
Iranian Pastor Hormoz Shariat is with International Antioch Ministries. He hosts a satellite television show that is broadcast into Iran.
"Most often the Revolutionary Guards arrest and don't even tell their family. They can't have a lawyer, not even a formal charge. Sometimes they get killed without even a formal charge," he explained.
When he became president in 2005, Mahmoud Ahmadinejad pledged to halt the spread of Christianity in Iran and launched a crackdown at that time.
But David Yeghnazar, the U.S. director of Elam Ministries, says the government's efforts are now intensifying.
"In particular in this last year, this persecution has gained momentum and I really think that is because the church is growing with increasing momentum," he explained.
Yeghnazar and Shariat say the government, for the first time, has admitted that Iranians are leaving the Islamic faith and becoming Christians.
"They are writing about it in the newspapers. They are warning people. They have stated publicly that they will arrest people who are becoming Christians, that they will close down networks of house churches," Yeghnazar said.
"The government is intentionally going after the house churches. The supreme leader last October came and said the house churches in Iran are a threat to our national security," Shariat told CBN News.
And that was a signal, Shariat says, for the government to target house church Christians -- especially their leaders.
According to the Iranian Christian news service, Mohabat News, Iranian Ayatollah Mesbah Yazdi has warned against the strong attraction of Christianity among Iranian youth. He recently admitted the government crackdown has failed to stop the spread of Christianity in Iran.
But Iran's Islamic government is likely to continue the crackdown. And many Iranians are worried that similar radical Islamic governments could arise in other Middle Eastern countries.
As revolutions and uprisings spread throughout the Middle East, Shariat says his Iranian viewers are warning Arabs to learn from what happened in Iran in 1979 when Iranians protested against the Shah and got Ayatollah Khomeini instead.
"They are telling their brothers and sisters, 'Watch out. Watch out. This is what we did. We wanted freedom. We wanted democracy, and we allowed the religious fanatics to take over. Please do not allow that to happen to you,'" he said.