The Christians – 46 women and six men including three church leaders – were arrested last Friday, February 8, said the well-informed Religious Liberty Commission of the World Evangelical Alliance, or 'WEA-RLC', which represents evangelical believers worldwide.
It said the three church leaders – two of them women – were produced in an Islamic court in the eastern city of Dammam on charges of converting Muslims to Christianity.
"We call on Saudi authorities to treat all those arrested with dignity, and release them immediately as there is apparently no evidence for any offense against them," said Godfrey Yogarajah, WEA-RLC's executive director.
"Arrest of believers for peacefully gathering for worship goes against the spirit of Saudi Arabia's promotion of inter-religious dialogue in international fora," he added.
This isn't an isolated incident in the Islamic kingdom. In December 2011, Saudi authorities detained 35 Ethiopian Christians, 29 of them women, for "illicit mingling," after security forces arrested them raiding a private prayer gathering in the eastern city of Jeddah, Christians said at the time.
Rights activists believe the women were subjected to arbitrary body cavity searches while in custody. Officials had no known comment.
Dammam, where last week's detentions took place, is known as a center for petroleum and natural gas.
Though foreign workers are active in the key region, they aren't free to worship, according to rights investigators. Locals are also under pressure, with reports that a Saudi girl who embraced Christianity fled Dammam in September 2012.
She was granted asylum in Sweden last month, WEA-RLC cited the Al-Yaum newspaper as saying.
"More than 10 years since the September 11, 2001 attacks on the United States, the Saudi government has failed to implement a number of promised reforms related to promoting freedom of thought, conscience, and religion or belief," noted the U.S. Commission on International Religious Freedom in its 2012 annual report.
"The Saudi government persists in banning all forms of public religious expression other than that of the government's own interpretation of one school of Sunni Islam; prohibits churches, synagogues, temples, and other non-Muslim places of worship; uses in its schools and posts online state textbooks that continue to espouse intolerance and incite violence; and periodically interferes with private religious practice," the report stressed.