The gardai are investigating claims that planes passing through Shannon Airport have been used for the CIA's so-called extraordinary rendition programme.
A Garda spokeswoman said a number of complaints received in recent years about activities at Shannon have been investigated.
"Some are completed and files have been sent to the DPP and others are ongoing but to date there have been no prosecutions," the spokeswoman said.
The long-running controversy over the US's use of Shannon in its "war on terror" resurfaced yesterday when a Council of Europe report found Ireland was complicit in the illegal detention and alleged torture of people seized by the CIA and flown to secret camps around Europe and North Africa.
The Government has accepted assurances from US President George W Bush that while CIA rendition flights exist, none have passed through Shannon with prisoners aboard.
But the Council of Europe report authored by Swiss senator Dick Marty substantiated long-standing claims that planes involved in rendition used Shannon for operational purposes, generally refuelling.
Mr Marty found the Co Clare airport had been used between 30 and 50 times but said he had no evidence of prisoners being aboard the planes, which were disguised as civilian aircraft.
The Government rejected yesterday's report but human rights groups and Opposition parties urged the Government to establish a regime for the inspection of aircraft suspected of involvement in human rights abuses and breaches of international law.
Garda and security sources have indicated that planes can be searched without warrant but that hard evidence would be required for such a course of action to be taken.
However, when the planes are owned by another sovereign state - even covertly - there are legal complications.
Meanwhile, World Airways, which transported over 175,000 US troops through Shannon this year, has elected to end its use of the airport and instead use Leipzig in Germany.