Researchers looking at the use of CIA-linked planes for prisoner transfers in the war on terror have found "conclusive" evidence of landings at Scottish airports.

An extensive database on so-called rendition flights compiled by a university team refers to 13 stops at Aberdeen, Wick and Inverness.

One aircraft that landed at Wick in 2004 has been "logged flying to secret prison and torture destinations", the researchers said.

The findings were made in work by two academics, Dr Ruth Blakeley at the University of Kent and Dr Sam Raphael at Kingston University in London.

The use of Prestwick, Glasgow and Edinburgh as a stop-off on journeys often linking the US and Middle East was already identified in their online database.

Five flights landed at Wick, a further five at Inverness and three at Aberdeen, according to the research.

The north and north-east links were not previously considered "suspicious" by the team, but were highlighted for further investigation after details of flight paths emerged.

"The Rendition Project database provides conclusive evidence that airports in the north of Scotland were visited by CIA planes at the height of the rendition and secret detention programme," Dr Raphael said.

It cannot be established if the planes had prisoners on board, only that aircraft were linked to rendition flights in the past.

The academics said rendition flights involve the transfer of suspects to locations abroad where they may have been tortured.

Their database has tracked more than 11,000 flights by more than 120 aircraft linked by past investigations to renditions.

A Scottish Government spokesman said: "The Scottish Government does not believe such flights could ever be in accordance with domestic or international law, and we would not expect such consent to ever be granted."

A spokeswoman at Aberdeen Airport declined to comment. No-one could be reached immediately for comment at Highlands and Islands Airports, which operates Wick and Inverness.