Iranian officials have arrested about 70 Christians since Christmas in a crackdown that demonstrates the limits of religious tolerance by Islamic leaders who often boast they provide room for other faiths.

The latest raids have targeted the small community of Iranian Christians who gather in house churches. Iranian officials have described them as “hard-liners” who pose a threat to the Islamic state. Authorities increasingly view them with suspicions that range from trying to convert Muslims to being possible footholds for foreign influence.

Christian activists claim their Iranian brethren are being persecuted simply for worshipping outside officially sanctioned mainstream churches.

Iran’s constitution gives protected status to Christians, Jews, and Zoroastrians, but many religious minorities sense growing pressures from the Islamic state as hard-edged forces such as the powerful Revolutionary Guard exert more influence.

In past years, authorities have staged arrests on Christians and other religious minorities, but the latest sweeps appear to be among the biggest and most coordinated.

Iranian Christians have congregated in house churches in order to avoid the monitoring of sanctioned churches from Islamic authorities, who have kept closer watch on religious minorities since the chaos after President Mahmoud Ahmadinejad’s disputed election in 2009.

Groups monitoring Christian affairs in the Islamic world say Iranian authorities see the unregulated Christian gatherings as a potential breeding ground for political opposition—Tehran Governor Morteza Tamadon suggested that the Christians could have links to Britain—and suspect they may try to convert Muslims in violation of Iran’s strict apostasy laws.

The wave of arrests began Christmas morning, and since then opposition websites have reported 70 Christians arrested, including those regarded as pastors in the house church movement. Many were later released, but the reports say more than a dozen remain in detention and officials have hinted more raids are possible.

There are no accurate figures on the number of Christians in the “house church” movement or followers outside established denominations. But the manager of the Iranian Christian News Agency, Saman Kamvar, said authorities likely perceive some kind of challenge to the religious status quo and are “feeling insecure.”

The Associated Press contributed to this report.