Iranian authorities have reportedly arrested over 100 Christians in the past few days, as they seek to crack down on conversions and what they claim is proselytizing by evangelicals.

Citing Open Doors UK, a charity that monitors persecution of Christians around the world, the Telegraph reported Monday that growing public interest in the minority faith, which makes up less than 1 percent — or around 350,000 — of the population, has worried the Islamic regime, leading to to crackdowns on churches and congregants.

While the existing Christian minority is accepted by Iran’s rulers, conversion from Islam is a punishable offense.

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“This spike in arrests is highly concerning,” Zoe Smith, head of advocacy at Open Doors, told the paper. “It follows an established trend of the Iranian government: as the number of converts to Christianity increase, so the authorities place greater restrictions on churches.

“The restrictions are worse for churches seen to be attended by Christians who have converted from Islam. Not only that, but the government is asking unreasonably high bail amounts and seeing longer prison terms for Christians.”

She added that Church leaders are being “put under pressure to leave the country or face an arrest.”

Rights groups such as Human Rights Watch and Amnesty International have criticized Iran for its mistreatment of Christian converts, as well as other religious and ethnic minority groups.

Prime Minister Benjamin Netanyahu has lambasted Iran on several occasions for its treatment of Christians. In July he said Iran was torturing and jailing Christians in a “brutal” persecution campaign. Last Christmas he mocked Iran’s foreign minister for posting holiday greetings on Twitter.

“Saying ‘Merry Christmas’ while jailing Christians in your own country is the height of hypocrisy,” Netanyahu said.

Raphael Ahren contributed to this report.