Scotland's leading prosecutor has ordered police to investigate new claims that Scottish airports are used as stop-off points for CIA rendition flights from around the world.

An academic study claims to have conclusive evidence that suspects being transferred by private jet to face torture in secret prisons are landing in Scotland. Lord Advocate Frank Mulholland QC said the study will now be investigated fully.

The study says that, in addition to other Scottish airports, five flights landed at Wick, a further five at Inverness and three at Aberdeen.

Mr Mulholland's move was welcomed by campaigners, but the Scottish Human Rights Commissioner, Professor Alan Miller, warned the inquiry should not simply involve "plane-spotters being interviewed" and had to find out what happened and prevent any recurrence.

He said: "The Scottish Human Rights Commission has for some time now been demanding an official investigation into these increasing reports. The UK has ratified the UN Convention against torture and this requires mechanisms to ensure future compliance."

Green MSP Patrick Harvie also pointed out that previous investigations into alleged rendition through Prestwick got nowhere.

"This sounds like a step in the right direction but what we need is for any investigation and prosecution to be proactive," he said. "There is no other area of serious, organised crime where we would take such a passive attitude."

SNP MSP Rob Gibson said he had been asking questions since 2005 about possible rendition flights passing through his Highland constituency.

He added: "I am delighted there will be an investigation into what has happened at Wick and other airports. There must be people who have information on the refuelling of such flights and I am sure the police will follow up this lead."

Dr Ruth Blakeley of the University of Kent and Dr Sam Raphael of Kingston University, in Surrey, said they have compiled an extensive database of rendition flights in Scotland.

The use of Prestwick, Glasgow and Edinburgh as a stop-off on journeys often linking the US and the Middle East was already identified in their database, but details of landings at Wick, Inverness and Aberdeen are new.

Mr Mulholland told MSPs: "It is very important that there should be no dilly-dallying in this matter. I am confident that the police will conduct a thorough inquiry. The use of torture cannot be condoned. It is against international law and contrary to the common law of Scotland."

He said a police inquiry into allegations of extraordinary rendition at Scottish airports in 2007 and 2008 concluded there was insufficient evidence to start a criminal investigation.

Mr Mulholland said new information and any other details that emerge about rendition flights since that inquiry would be forwarded to investigating officers.

He warned a high standard of proof would be needed for criminal proceedings to take place, and added: "Speculation, conjecture, innuendo and belief are insufficient. What you need is hard evidence, sufficient evidence to the requisite high standard of proof."

Police Scotland Deputy Chief Constable Iain Livingstone said: "We have been in liaison with the Crown Office and Procurator Fiscal Service today and are aware that we will receive formal instruction on this matter. Once that instruction is formally received, we will consider it and report back."

The links to the north and north-east of Scotland were not previously considered suspicious by Dr Blakeley and Dr Raphael but were highlighted for further investigation after details of flight-paths emerged.

One aircraft which landed at Wick in 2004 has been "logged flying to secret prison and torture destinations", the researchers said. It cannot be established if the planes had prisoners on board, only that aircraft were linked to rendition flights in the past.