A federal judge has denied motions by the US government and telecoms provider AT&T that sought to block a lawsuit centring on the the carrier's alleged cooperation in a government wiretapping programme.

The suit was brought forward last January by the Electronic Frontier Foundation (EFF), which claims that AT&T illegally allows the National Security Agency to listen in on traffic on its network.

The US government was asking for a dismissal of the case because it could expose state secrets.

It argued that the wiretapping programme, if it exists, is a state secret. Additionally it was claimed that any evidence arising from the case would also be secret, so preventing AT&T from staging an effective defence.

The judge, however, ruled that the existence of the case is already common knowledge and by itself cannot be considered a state secret.

He proposed appointing an independent expert to determine whether evidence should be considered a secret.

The EFF praised the ruling. "Judge Walker correctly found that the government, after having already admitted to and extensively commented on the NSA's spying programme, cannot now claim that it is a secret and sweep AT& T's role under the rug," said EFF staff attorney Kevin Bankston.