Danish broadcaster DR reports the connection based on independent anonymous sources.
The collaboration is described in the report as a top-secret collection of a large amount of raw data from cable access given by FE to the NSA.
The cable in question is used for all types of digital communication including telephone calls, internet and SMS messaging, DR reports.
As such, NSA may have been given access to data which could have included Danish citizens' private personal information and communication.
Both the Danish Ministry of Defence and FE have declined to comment on connections between the watchdog report and cooperation with the NSA.
“The audit of FE has raised several serious points of criticism. This is a serious issue. The watchdog has recommended an inquiry be initiated. The government will be furnished with the basis for this inquiry. So that investigation should be allowed to take place, and I have no further comment until it is complete,” Prime Minister Mette Frederiksen said when asked about the DR report.
Criticisms made public by the watchdog, TET (Tilsynet med Efterretningstjenesterne) earlier this week include the contention FE may have passed on a “significant amount of information about Danish citizens” in breach of the country’s laws.
NSA has not commented on the matter.
DR has not been able clarify exactly when the reported cooperation with the NSA began and whether it still exists. But the broadcaster reports that it was an “extremely valuable collaboration” for FE.
It has also not been possible for DR to clarify whether the NSA cooperation is legal or illegal. Several current and former senior FE staff have been suspended due to the TET report.