A health board has apologised for "past failings" after a probe following the deaths of five babies at one hospital found evidence of sub-optimal care in those cases.

The deaths are examined in a review of the safety of neonatal services at Caithness General Hospital published recently by NHS Highland.

An external independent inquiry featured in the report considered the two stillbirths and three neonatal deaths from 2010 to 2015 and concluded that at least two of the deaths were "potentially avoidable".

"Sub-optimal care" and "avoidable factors" were recorded in all five of the perinatal deaths analysed.

It comes a week after the Scottish Government ordered a review following six so-called "unnecessary" deaths of babies at Crosshouse Hospital in Kilmarnock, East Ayrshire, since 2008.

Scottish Labour has called on ministers to announce a national review of staffing and workforce issues across all maternity units.

The comprehensive 116-page report into maternal and neonatal services at Caithness General Hospital will be discussed on Tuesday at a meeting of the NHS Highland board.

It recommends that Caithness Maternity Unit should operate as a midwife-led Community Maternity Unit (CMU) on the grounds of safety, while cases with a risk of complications should go to Raigmore Hospital in Inverness.

The review was prompted by the potentially avoidable death of a newborn baby at the hospital in September last year.

NHS Highland's medical director Dr Roderick Harvey, who ordered the review, said: "Families do rightly put their faith in the health service and the fact that infants died possibly as a result of sub-optimal care is unacceptable and I apologise unreservedly for these past failings.

"That is why I commissioned the current review and I would wish to assure you that the families have been uppermost in our minds when conducting the review.

"Having identified real safety concerns in my view we must move swiftly to address these concerns and that is the basis of my recommendations."

There have been no legal claims over the deaths, the health board confirmed.

No members of staff have been disciplined as a result of the five deaths because "any identified deficiencies did not reflect on individual clinicians, but rather the system that they work in".

Last week, Health Secretary Shona Robison instructed Healthcare Improvement Scotland (HIS) to carry out a review into certain cases in Ayrshire and Arran "to inform me whether the correct procedures and processes were properly followed".

Between 2008 and March 31 this year, there were four Significant Adverse Event Reviews concerning stillbirth deaths at Ayrshire Maternity Unit at Crosshouse Hospital, said NHS Ayrshire and Arran.

The BBC said there have been six so-called "unnecessary" deaths of babies at the hospital since 2008.

Labour health spokesman Anas Sarwar said: "These reports are heart-breaking, and our thoughts are with every family who has been affected by the death of a child.

"The report in Caithness and review at Crosshouse follow on from figures which revealed 25,000 incidents in maternity wards across Scotland since 2011."

He added: "Labour wants to see the Scottish Government launch a national review of staffing and workforce issues across all maternity units."

Health secretary Shona Robison said: "The safety of mothers and their babies is of paramount importance, which is why we must do everything we can to mitigate against similar incidents happening again.

"Our deepest sympathies go out to the families who have been affected.

"We want to ensure that every woman and baby in Scotland gets the best maternity and neonatal care and that is why we initiated a review of maternity and neonatal services across Scotland, which will report shortly.

"Healthcare Improvement Scotland is conducting a review into the cases in Ayrshire and Arran to inform me whether the correct procedures and processes were properly followed in these cases.

"If there are lessons to be learned or improvements which need to be made, we will not hesitate to act.

"We are aware of the report into the safety of Caithness maternity and neonatal services commissioned by NHS Highland. The Chief Medical Officer supports the findings of the report on clinical grounds."

Robison added: "It is critical that NHS Highland responds to concerns raised by local people, particularly on the issues of ambulance transfer from Caithness and facilities at Raigmore for families, when making a decision on the future of services."