ISLAMABAD (AP) — An Afghanistan-based nonprofit said Saturday it is working with the United Nations and others for the swift release of 18 staffers, including a foreigner, detained by the Taliban.

The International Assistance Mission said the 18 people were detained on two separate occasions this month from its office in central Ghor province and taken to the capital, Kabul.

Local media reported that a U.S. national is among those detained and that staff members were detained for preaching about Christianity. The nonprofit said it still has 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,” the nonprofit said. “We are also working with the U.N. 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.”

The mission said it values and respects Afghanistan’s customs and cultures, standing by the principle that aid will not be used to further a “particular political or religious” point of view. It said all its staff agree to abide by the country’s laws.

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

The nonprofit said two Afghan nationals and one international team member were taken from its Ghor office on September 3. A further 15 Afghan national staff members were taken from the same office on September 13.

NGOs have come under greater scrutiny since the Taliban seized 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 U.S. watchdog reported earlier this year that the Taliban are harassing NGOs operating in the country.