The Royal College of Nursing (RCN) Scotland has called for more investment in mental health services after figures revealed the number of specialist nurses has fallen.

A report by the organisation found that the NHS in Scotland lost 64 mental health nurses between 2011 and 2014.

The RCN said the drop was particularly concerning as 38% of the current workforce are over 50 and can retire in the next five years.

The report highlights a 17% fall in the number of available beds in mental health services since 2010 and a 6% decrease in inpatient admissions.

It says: "The reduction in the mental health nursing workforce is a concern in Scotland, particularly given the profile of the ageing workforce.

"A reduction in inpatient admissions and inpatient beds within mental health services does not mean that there can simply be a reduction in the numbers of nursing staff to improve outcomes for people with mental illness.

"While more patients are now being treated in the community, the patients that do require inpatient services now have more complex needs.

"This means that there may actually need to be an increase in the number of nurses on mental health wards to cope with the increase in patient acuity."

Norman Provan, RCN Scotland associate director, said: "The good news is that there's been a reduction in the number of patients being admitted to hospital and more patients experiencing mental health problems are now being treated in the community.

"However, those patients who do need treatment in hospital now have much more complex needs. This means that we need to see an increase in the number of nurses on mental health wards, to cope with and help treat those experiencing increasingly complex mental health problems."

The organisation also raised concerns about the pressures on meeting Scottish Government targets for access to psychological therapies and for mental health services for children and adolescents.

Mr Provan added: "The Scottish Government has just announced a three-year innovation fund for mental health. This is a step in the right direction and there are some great examples of innovative nurse-led services in Scotland, which are improving the lives of patients with mental health issues.

"We know money is tight in the NHS, but if we are serious about treating mental illness in the same way as physical illness, then we need long-term sustainable investment in the future mental health workforce and in the short term, we need to make sure we have enough mental health nurses with the right skills to care for patients in the community and in hospitals.

A Scottish Government spokeswoman said: "By protecting the frontline budget of the NHS in Scotland we've ensured that the overall number of mental health nursing staff has increased by 600 in the last five years.

"We recognise that mental health services, particularly those focused on children and young people, are key to the quality of life of many of the most vulnerable people in our society. That's one of the reasons we announced an additional investment of £15 million this week in mental health services to ensure that people get the help and support they need.

"We look forward to working with stakeholders, like the RCN, as we shape how the extra funding would be best directed to address the demand for services."

The Scottish Liberal Democrats called on First Minister Nicola Sturgeon to make a statement of intent on mental health services by backing their call for a new Bill which would guarantee that people with mental illness are treated equally to those with physical illness.

The proposal was put forward by party leader Willie Rennie at their conference this weekend.

Referring to the RCN's report, party health spokesman Jim Hume said: "This demonstrates that the Scottish Government's funding commitment of £15 million over three years may only be a drop in the ocean of what is required to improve Scotland's struggling mental health services.

"With a 17% fall in the number of beds available in mental health services and a loss to Scotland's NHS of 64 mental health nurses, urgent action is needed to bolster services which some one in four people may need access to at some point in their lives.

"I want the new First Minister to make a statement of intent on mental health services by backing our calls for a new law to place the treatment of mental and physical ill health on an equal footing.

"This step would mandate ministers and health agencies to take action."