The Taliban are going to door-to-door and arresting government employees and Afghans who have worked with the US and UK.
Militants are carrying out a methodic hunt for certain people who collaborated with foreign forces, Christian Nellemann, director of the Norwegian Centre for Global Analyses, told the BBC.
He said: “What we have seen is that the Taliban, in advance of moving into all major cities in Afghanistan, not just Kabul, is that they have a more advanced intelligence system.”
“They have lists of individuals and even within the very first hours of moving into Kabul they began a search of former government employees – especially in intelligence services and the special forces units.”
Nellemann’s organisation provides intelligence to the UN.
There were fears this could lead to mass killings alongside exposing “the intelligence networks that the West has provided,” Nellemann added.
In a briefing to the UN, the Norwegian Centre for Global Analyses said the Taliban were recruiting new informer networks to work with their regime.
An interpreter who had worked with foreign troops and government aid agencies told the BBC World Service his fear now he was stuck in the country under Taliban rule.
Speaking under the alias Jay, the interpreter said militants had searched his house, messaged him and told him he was “the leader of the enemies of the Taliban”.
He added: “They have seized my house, I’m not going to go there again, but it’s not enough for them. They’re looking for my life and the life of my family and that’s exactly what they will be doing with every ally of the international forces.”