US government attorneys filed an appeal on Monday against a Chicago trial judge's decision to grant lawyers for a terrorism suspect unprecedented access to secret intelligence - court records that they say might help his defense.

The government appeal argues that the judge's decision, if upheld, would represent a "sea change" in how such sensitive documents are handled and could end up jeopardizing US national security.

The dispute relates to the case of Adel Daoud, a 20-year-old US citizen from a Chicago suburb who denies allegations he took a phony car bomb from an undercover FBI agent in 2012, parked it by a downtown Chicago bar and pressed a trigger.

In the surprise ruling in January, US District Judge Sharon Johnson Coleman said defense attorneys could examine an application submitted to the Foreign Intelligence Surveillance Court, or FISA court, which was established in 1978.

Coleman's ruling would allow defense attorneys to comb through the government's application asking the secret court to allow the FBI and other agencies to spy on Daoud as part of the government's investigation.

The application to the FISA court could indicate what led investigators to decide Daoud should be scrutinized further, be it an informant or the type of widened surveillance revealed by former National Security Agency contractor Edward Snowden.

Coleman's ruling in January was the first time a judge had allowed defense attorneys to examine the secret material in defending a client facing terrorism charges.

Fair trials

In her ruling, she said allowing defense attorneys to vet all potential evidence against their clients was the "bedrock" of the Sixth Amendment's guarantee that defendants will get a fair trial.

The legal debate about whether secret court documents will be shown to Daoud's attorneys is being watched by other lawyers defending terrorism suspects. In their 35-page appeal filing, lawyers for the government described the secret documents as dealing with "exceptionally sensitive issues with profound national security implications".

If permitted to stand, the district court's order would put prosecutors in "a lose-lose dilemma", the appeal said.

"Disclose sensitive classified information to defense counsel - an option unlikely to be sanctioned by the owners of that information - or forfeit all FISA-derived evidence against the defendant, which in many cases may be critical evidence for the government."

Daoud's attorney, Thomas Durkin, singled out prosecutors' reference to unnamed "owners" of the information, saying the phrasing appeared to suggest someone other than the US Justice Department was calling the shots about what could and couldn't be disclosed in a criminal case.

"It's astounding," said Durkin in a phone interview later on Monday. "This proves what I have been saying all along, which is that the Justice Department and the US attorney's office are not running this case. This is a case being run by the NSA or the CIA or whoever is the owner of that information."

Unsurprisingly, perhaps, for a government document on secrecy, whole sections of the appeal filing were secret. Underneath one titled "The FISA Applications Established Probable Cause" were the words, "CLASSIFIED MATERIAL, REDACTED".