While federal authorities have yet to take over the case from state prosecutors in Saxon capital Dresden, the investigation is a step towards the group facing a trial at the federal level.
The files cover two cases against a total of five men and one woman aged between 18 and 40.
They are accused of attacking refugee accommodations and refugee aid workers.
Dresden-based prosecutors had flagged up the case to their federal colleagues in Karlsruhe because they suspected it could qualify for the serious crime of “forming a terrorist group”.
One of the two cases concerns an attack on an asylum accommodation centre on the outskirts of Freital, which became notorious in summer 2015 as a hotspot of anti-refugee sentiment after weeks-long demonstrations against refugee accommodations and repeated attacks against asylum seekers.
The case also covers an attack using explosives and butyric acid against an “alternative living project” for refugee supporters in Dresden.
The state trial against the five suspects – men aged 18, 24, 27 and 29, and a 27-year-old woman – had been due to start imminently, but the charges were withdrawn to allow the federal prosecutors time to examine the files.
One of the accused in the first case, the 27-year-old man, is also believed to have been involved in a case of serious bodily harm against refugee supporters.
He and two other men are accused of a baseball bat attack against people who took part in a welcome demonstration in Dresden last summer.
One of the victims was the son of the deputy Minister-President of Saxony, Martin Dulig.
Police raids by the Politically Motivated Crimes Unit (PMK) and Anti-Extremism Unit (OAZ) in Freital and Dresden in November and March turned up explosives, Nazi memorabilia and computers.
The OAZ released figures on Tuesday reporting that it had investigated 208 cases with a far-right political background and solved 123 of them in 2015, broadcaster MDR reported.