The UN definitely acknowledges the existence of terrorists groups

Expressing grave concern that foreign terrorist fighters who have joined entities such as (ISIL), the Al-Nusrah Front (ANF) and other cells, affiliates, splinter groups or derivatives of ISIL, Al-Qaida or other terrorist groups, may be seeking to return to their countries of origin or nationality, or to relocate to third countries, and recognizing that the threat of returning or relocating foreign terrorist fighters includes, among others, such individuals further supporting acts or activities of ISIL, Al-Qaida and their cells, affiliates, splinter groups, and derivative entities, including by recruiting for or otherwise providing continued support for such entities, and stressing the urgent need to address this particular threat,

I couldn’t find a list either but there’s not a lot of documents under the “Foreign terrorist fighters” category -> https://www.un.org/counterterrorism/un-documents