Reports of an unexpectedly high number of deaths at Aberdeen Royal Infirmary's intensive care unit are under investigation.

Medics predicted 150 deaths at the ICU in 2015, which would have given a "mortality ratio" of 1.0.

A higher number of deaths pushed this up to 1.2 - the worst of any ICU in Scotland, according to the Scottish Intensive Care Society Audit Group (SICSAG).

The actual number of deaths was not revealed.

NHS Grampian said it believes an auditing error is responsible and has commissioned an external review.

A spokeswoman said: "We have examined our audit process and believe there is a data entry issue which has contributed to these figures.

"We are working to resolve that error to ensure that these figures more accurately reflect patient data in the intensive care unit in the future.

"We are also aware that there are often other complex underlying factors which may influence these figures and so in order that we can provide assurance to patients, relatives and staff, we have also commissioned a further external review of the data and the unit which will report shortly.

"The intensive care unit at Aberdeen Royal Infirmary offers first-class specialist care and treats patients from Aberdeenshire, Moray as well as the north of Scotland including Orkney and Shetland."

Glasgow Royal Infirmary ICU has the lowest mortality rate, according to SICSAG.