US authorities intercepted and recorded millions of phone calls last year under a single wiretap order, authorized as part of a narcotics investigation.

The wiretap order authorized an unknown government agency to carry out real-time intercepts of 3.29 million cell phone conversations over a two-month period at some point during 2016, after the order was applied for in late 2015.

The order was signed to help authorities track 26 individuals suspected of involvement with illegal drug and narcotic-related activities in Pennsylvania.

The wiretap cost the authorities $335,000 to conduct and led to a dozen arrests.

But the authorities noted that the surveillance effort led to no incriminating intercepts, and none of the handful of those arrested have been brought to trial or convicted.