Iran has 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 grass-roots Christian groups Iran describes 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.

Caught in the middle is the small community of Iranian Christians who get together for prayer and Bible readings in private residences and out of sight of authorities. They are part of a wider "house church" movement that has taken root in other places with tight controls on Christian activities such as China and Indonesia.

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.