Environment Secretary Roseanna Cunningham has condemned the "deliberate and sustained" persecution of birds of prey after a new report showed almost a third of golden eagles tagged in Scotland vanished in suspicious circumstances - with illegal killing the most likely explanation for their disappearance.

She told MSPs the new report "provides clear evidence" of illegal behaviour, with "clusters of disappearances" associated with some grouse moors in the Highlands

She pledged action to tackle the problem, including the publication of a map revealing six clusters where birds have gone missing, and working with Police Scotland to pilot the use of special constables in the Cairngorms National Park.

Government officials will also be working with Scottish Natural Heritage, which produced the report, to look at how existing powers could be used to order a temporary or permanent halt on activities on grouse moors where there is "good reason to believe they are harming highly-protected raptor species".

But the Scottish Government has ruled out giving the Scottish SPCA more investigative powers.

There were 131 golden eagles tagged in Scotland between 2004 and 2016, with the Scottish Natural Heritage report stating 10 died of natural causes, five were killed, while the tags on 41 birds were recorded as having stopped without malfunctioning.

The report said: "It was apparent that satellite tagging of young golden eagles revealed that many young birds have probably been illegally killed in some parts of Scotland between 2004 and 2016, largely in the central and eastern Highlands."

It added that "the results strongly indicated that this was due to human influences operating primarily in six clusters, mostly in the central and eastern Highlands".

It concluded: "A relatively large number of the satellite tagged golden eagles were probably killed, mostly on or near some grouse moors where there is recent, independent evidence of illegal persecution.

"This illegal killing has such a marked effect on the survival rates of the young birds."

Ms Cunningham, who commissioned the research last year, said the report is "extremely concerning".

She added: "Its conclusion is that illegal killing is the most likely explanation for the disappearance of these birds, and that there are clusters of disappearances associated with some driven grouse moors.

"This report provides clear evidence of deliberate and sustained illegal persecution in some parts of Scotland associated with driven grouse shooting."

Labour Highlands and Islands MSP David Stewart: "I am disappointed she is not willing to extend the powers of the Scottish SPCA inspectors to investigate wildlife crime.

"Given the new evidence about the appalling scale of persecution of Scotland's birds of prey, surely extending this power is a power whose time has come. We need to investigate more, not less."

Ian Thomson, head of investigations at RSPB Scotland, said the report is a "damning indictment of Scotland's driven grouse shooting industry", adding that the "scale of systematic, organised criminality, is shocking".

Susan Davies, director of conservation at the Scottish Wildlife Trust, said the report is "further proof of the need for a step-change in the way our uplands are managed, including the introduction of a licensing system for driven grouse moor management to address wildlife crime and encourage more sustainable stewardship of these areas".

A Scottish Gamekeepers Association (SGA) spokesman said: "Losing, on average, four tagged eagles per year across Scotland is totally unacceptable. The illegal killing of any eagle is condemned wholeheartedly by the SGA and all law abiding gamekeepers.

"Although this study assimilates 12 years of evidence and makes difficult reading, it does acknowledge recent improvements in some grouse moor areas previously associated with suspected persecution."

While he said conservation efforts have improved, he added that "problems clearly still exist in some hotspot areas".

While the report said wind farms are "not associated with any recorded golden eagle deaths", the SGA spokesman said it did "not believe the report adequately tackles the threat wind farms pose to raptor species as there is a significant amount of published data from other countries which show a negative correlation between bird survival and turbine strike".

But he added: "That is not an attempt in any way to detract from the report's findings."

David Johnstone, chairman of Scottish Land and Estates, said the report is "challenging reading" for the grouse shooting industry - though he pointed out "satellite tags have also stopped working in areas where grouse moors are not located".

But he made clear: "Action needs to be taken against wildlife crime and we believe a two-fold approach of punishment and prevention is the most effective way forward.

"We look forward to putting forward with vigour our own proposals for increased punitive and preventative measures that we think can make a difference.

"There has been much heated debate over this issue recently and it is essential that whatever action is taken going forward, it is based on evidence and clear thinking rather than any inherent prejudice against game shooting."