Relatives say they have been unable to meet with them, and authorities have refused to specify the charges against them. Fereshteh Dibaj and her husband Reza Montazami -- known as Amir to family and friends -- led an independent church in the city of Mashhad.
Plainclothes security agents arrested 28-year-old Dibaj and 35-year-old Montazemi early on September 26 after searching their home and confiscating the couple's computer, Christian books, and other belongings.
One of the agents told Montazemi's mother that her son was being taken to a local police station. But when relatives went to the police station, a policeman on duty said he was unaware of the detentions.
After hours of search and inquiry, the family learned that the Information Ministry was holding the couple for questioning.
More Questions Than Answers
Authorities have so far refused to comment on the reason for the detentions or the charges against the couple.
Fereshteh's brother, Issa Dibaj, lives in the United Kingdom.
"In Iran they first arrest people, then they look for charges," Issa Dibaj told RFE/RL. "So far [authorities] have not announced charges against them -- they said, 'We are investigating and questioning them.' They let Amir make a short call to his family to say he is well. But Fereshteh has not been allowed to telephone, and, since her detention a week ago, we have had no news from her and we are very concerned. They haven't even let her talk to Christine, her 6-year-old daughter."
Montazami converted to Christianity in his early 20s.
His wife, Fereshteh, was born into a Christian family. Her father Mehdi Dibaj was a well-known priest of the Jamiat-e Rabbani Church, the Iranian branch of the Assemblies of God. He spent more than nine years in prison and was sentenced to death in 1993 for his faith. He was freed in January 1994 in the face of an international outcry. But a few months later, he was abducted and later found murdered -- one of at least three priest killings that activists blame on Iranian authorities.
Issa Dibaj said the couple had received a warning in connection with their religious activities.
"[Authorities] had told them that they should not have prayer meetings in their house. But how is that possible?" he asked. "Just as Muslims are free anywhere in the world to go and pray in a mosque, Christians should have the same right -- this is a [fundamental] right. Maybe one reason [for their arrest] is that they continued having these sessions as before."
For some, the case highlights the plight of Christian converts living in Iran.
Islamic law -- as applied in Iran -- says a Muslim who converts to another faith can face the death penalty. In recent years, there have been no reported cases of execution of converts.
But there are signs that pressure on Christians has increased.
Several Christian converts have been arrested in Iran in recent months before being freed on bail. There have also been allegations by religious and rights groups of harassment and intimidation targeting Christians.
In its annual report on religious freedoms in September, the U.S. State Department accused the Iranian government of enforcing its prohibition on proselytizing by evangelical Christians by closely monitoring their activities, closing their churches, and arresting converts.
The report said that in November 2005, unidentified attackers killed a man, Ghorban Tori, who had converted to Christianity more than 10 years earlier. Tori, a pastor at an independent house church of converted Christians, had reportedly been receiving death threats.
Issa Dibaj said he thinks the recent pressure and persecution of Christians is unprecedented since a string of killings of priests in the mid-1990s.
"In the last two years, maybe with the coming to power of a new president (Mahmud Ahmadinejad in 2005), pressures have increased in an unprecedented way," he said. "We had not seen anything like that since the chain killings that happened in 1994 and afterward -- Christians have lived relatively in peace. But in recent years, pressure has increased. There are arrests, threats, and sometimes they fire [Christians] from their jobs."
'They Cannot Fully Live Their Lives'
Prague Roman Catholic Bishop Vaclav Maly told RFE/RL after a September trip to Iran that many of Iran's Christians are leaving the Islamic republic because of restrictions -- and because "they cannot fully live their lives as Christians."
"There is a danger that Christians could completely disappear from Iran, which would be a great spiritual and cultural pity -- because Christians were on Iranian territory before Islam was, and there are very old churches there whose histories go back to the first century of Christianity," Maly said.
The number of Armenians, Iran's largest Christian minority, has significantly declined.
There are no reliable figures on the number of Muslim-born Iranians who convert to Christianity, and many practice their faith clandestinely for fear of state persecution. Christian groups claim the ranks of converts to Christianity is increasing nevertheless.
The perceived trend of official harassment is likely to add to the mounting concerns as family and friends worry over the fate of Fereshteh Dibaj and her husband.