An Afghanistan-based nongovernmental organization (NGO) said on Saturday it was working with the United Nations and a coordinating group for the swift release of 18 of its staff, including a foreigner, detained by the Taliban.

The International Assistance Mission (IAM) said the staffers were taken from its office in Afghanistan’s central Ghor province on two separate occasions this month and brought to the capital Kabul.

Local media reported that an American is among those detained and that the staff members were detained for preaching about Christianity. The nonprofit said it still had no information about the nature of the allegations.

“IAM has written to the Ministry of Economy, where we are legally registered as an international NGO, about these extremely concerning developments,” it said.

“We are also working with the UN and Acbar, the coordinating body for NGOs in Afghanistan, to deepen our understanding of the situation and to work for the quick release of our 18 colleagues,” it added, using the acronym of the Agency Coordinating Body for Afghan Relief & Development.

The mission said it valued and respected Afghanistan’s customs and cultures, standing by the principle that aid would not be used to further a “particular political or religious” point of view. All its staff agree to abide by the South Asian country’s laws, it added.

Afghan officials were not immediately available for comment on the detentions.

IAM said two Afghans and one international team member were taken from its Ghor office on September 3. Fifteen additional Afghan staffers were taken from the same office on September 13.

NGOs have come under greater scrutiny since the Taliban retook control of the country two years ago. They have introduced harsh measures, including banning Afghan women from education beyond sixth grade and barring them from public life and work, including jobs at NGOs.

A United States watchdog reported earlier this year that the Taliban are harassing NGOs in the country.