Open Doors is asking Christians to pray after the Taliban seized control of Afghanistan.
Afghanistan is ranked number 2 on the Open Doors World Watch List of the 50 places where Christians suffer the greatest persecution for their faith. The country is second only to North Korea.
The non-profit, which supports persecuted Christians around the world, said Afghanistan is home to a "small group of secret believers" for whom levels of vulnerability have "increased tenfold".
It said it is closely monitoring the situation as it called Christians around the world to join together in "urgent prayer" for the country.
"It's a heartbreaking day for the citizens of Afghanistan and an even more dangerous time to be a Christian," said Brother Samuel, Open Doors Field Director for Asia.
International Christian Concern said the fall of Kabul has "sparked a wave of new religious freedom concerns across the Middle East".
Claire Evans, ICC's Regional Manager, said the dramatic events of the last few days marked a "turning point" for religious freedom across the entire region.
"The atmosphere throughout the Middle East region has changed with the fall of Kabul to the Taliban," she said.
"The Middle East had just entered the recovery stages following the defeat of ISIS, an ideology predicated on the genocide of religious minorities.
"Now those same terrorists feel empowered by the Taliban's resurrection and success in Kabul.
"When ISIS captured new territory, Middle Eastern governments largely condemned it.
"Now, particularly in the case of Turkey, we see similar activities openly legitimized. This is potentially a significant turning point for religious freedom across the Middle East.
"We are watching the Middle Eastern response closely and with great concern."