Yemeni police have detained at least nine people this year for converting from Islam to Christianity, a security official said Tuesday.

The nine were arrested between May and early August and remain in police custody, said the official.

Converting from Islam to any other religion is illegal in Yemen and can be punishable by death. But in previous cases, those arrested are usually released after they revoke their new faith and pledge to return to Islam.

Three of the nine were detained in west of the capital, San'a, said the official, who spoke on condition of anonymity because he was not authorized to speak to the media. He declined to provide details about the others.

A family member of one of the detained said he fears those arrested could face torture or abuse in prison. The family member, who declined to be named because of security concerns, said Hani el-Dahayni, 30, was detained in May after police stormed his office and confiscated computers and compact discs.

Separately, police detained six Iranians who are followers of the Baha'i faith and have lived in Yemen for three decades, the security official said. The six were accused of being members of a rebel group, he said.

Though not officially banned in Yemen, the Baha'i religion is considered by some Muslims as heresy.

The Baha'i faith was founded by the Persian nobleman Baha'u'llah, who claimed to be a new prophet in the series that included Moses, Jesus and Muhammad. Islam considers Muhammad to be the last of the prophets.

Mansour Hayel, vice president of the Omar al-Gawi Political Forum that advocates for human rights and civil liberties in Yemen, blamed the arrests on the growing influence of extremist Muslim groups in Yemen.