The whereabouts of an Iranian Christian convert who was detained by Iran’s security forces more than a month ago is still unknown.

“Newly converted to Christianity, Aziz Majidzadeh was meeting his friends March 2 at their workshop near the city of Karaj when the security forces stormed the place,” spokesperson for religious freedom advocacy group Article 18, Kiarash Alipour, told Radio Farda.

Alipour said twenty other Iranian Christian converts were detained in a sweep around the same time as Majidzadeh. Their personal effects, including their cell phones and laptops, were confiscated.

According to the UK-based Article 18, which focuses its work on Christians in Iran, after lengthy interrogations, most of the detainees were released, but Mr. Majidzadeh is still being held in an unknown location.

Iranians born into families practicing minority religions in the Islamic Republic are generally tolerated and allowed to practice their faith, though they often face discrimination. However, converting from Islam to another religion, or apostasy, is considered a crime, and converts can face imprisonment and even execution.

Those who have converted to Christianity practice their faith in secret in so-called “home churches,” which are viewed with mistrust by the authorities. When arrested, Christian converts are usually charged with “actions against national security” for attending these secret home churches.

Though there are no official figures, rights groups say several Evangelical Christian converts have recently been sentenced to long prison terms in Iran.