Open Doors fears that a "systematic campaign" against Christians is underway in Algeria following the closure of a church and harassment towards believers.
It has described how members of the congregation at the Church of the Prince of Peace in Ighzer Amokrane put up a struggle when the authorities came to seal the building.
They occupied the church and refused to leave but the authorities came back again and this time were successful, with the church now having been closed since 2 September.
The l'Église Protestante d'Algérie (EPA), the legally recognised umbrella group of Protestant churches in Algeria, has condemned the move, calling it illegal. It added that the closure occurred despite not being ordered by any court.
It is not the first church to be closed in Algeria. In May, the authorities sealed off a church in the village of Boudjema, in the Kabilye area, while last year churches in Ait-Mellikeche, Al A'keed Amroush and Azaghar were also closed.
In another incident, the leaders of another EPA-affiliated church in Maatkas were summoned by the authorities and interrogated.
Since 2006, non-Muslim places of worship in Algeria have been required to have a licence but many EPA-affiliated churches report that it is only in the last two years that the authorities have started asking for proof that they have this.
At the same time, the authorities have ignored applications for new church licenses, while many existing churches have been issued with notices to cease activities.
Algeria is home to only 125,000 Christians - around 0.3% of the population. Converts face hostility from their families, while churches report interference and opposition from the authorities.
The country ranks 22nd on the Open Doors World Watch List of the 50 countries where Christians are the most persecuted.
A spokesperson for Open Doors said: "These actions clearly represent a deeply concerning continuation in the systematic campaign against Christians in Algeria.
"The National Commission for Non-Muslim Religious Groups, which was established by a 2006 Ordinance to issue official permits to churches, until now has not issued a single permit.
"These latest developments serve to undermine any sense that the Algerian authorities are taking genuine steps to improve Freedom of Religion of Belief in Algeria."