The NHS in Scotland will face "significantly more pressure" in the coming year despite a budget increase, doctors' leaders have warned.

The British Medical Association (BMA) Scotland claimed that "constrained resources" meant the health service was struggling to cope with increasing demands.

Chair Peter Bennie also raised fears the number of jobs lying vacant could have a "detrimental impact" on frontline care.

With Holyrood elections due to take place in May, Dr Bennie called on Scotland's political leaders to focus on the "serious challenges" the NHS has to deal with.

He said: "The funding gap faced by the NHS set against rising demand and the impact of increasing consultant, specialty doctor and GP vacancies and unfilled trainee posts cannot be ignored, and we must establish ways to make Scotland's NHS a more attractive place to work."

Dr Bennie made the plea as he issued his Christmas message just over a week after Deputy First Minister John Swinney announced the NHS would receive almost £13 billion in 2016-17 under his budget plans.

The BMA chair said that cash should help prevent the current funding gap from "growing further" but added: "It is clear that the NHS will face significantly more pressure as Scotland's population continues to age."

Public spending watchdog Audit Scotland "clearly identified that fundamental change is needed now if the NHS in Scotland is to cope with rising demands across a range of fronts", Dr Bennie said.

"The struggle to recruit and retain doctors adds to that burden significantly. Unfilled vacancies put pressure on existing NHS staff, already dealing with high workloads.

"This is a concern that doctors express to us regularly, along with the belief that in the long-term this will have a detrimental impact on their ability to deliver the sustainable, high-quality care people in Scotland need and deserve."

He insisted it is "not acceptable or sustainable" to rely on the goodwill of staff to "cover gaps in the workforce indefinitely".

Dr Bennie said: "How we respond is critical. Integration of health and social care is one of the major reforms facing healthcare delivery next year but again Audit Scotland has expressed its concerns about the progress of that implementation.

"The public will want to know that finite resources are being used in a way that optimises patient care and outcomes and their ability to access services.

"BMA Scotland's call to support Scottish general practice has also been recognised with the Scottish Government announcing increased investment in general practice.

"This is urgently needed as GPs face huge demands in workload with the number of doctors choosing to train as GPs falling and a number of senior GPs set to retire in the near future.

"Extra funding for primary care development will be vital to support Scottish general practice as demand on community-based services continues to increase."

He continued: "The focus must be on delivering high-quality care to the people of Scotland and ensuring our NHS is sustainable for future generations.

"We will ensure that doctors' voices are heard and continue to influence positive change.

"Their role is vital, not only in providing services today but in establishing how resources are used in the future to secure better outcomes for patients and to deliver a sustainable and flourishing NHS for Scotland."

Health Secretary Shona Robison said: "We agree with the BMA that the focus must be on delivering high-quality care to the people of Scotland and ensuring our NHS is sustainable for future generations

"That is why the Scottish Government has a clear vision for the future of our NHS and we will continue to take the right action to ensure that Scotland continues to have an NHS that it can be proud of today and in the future.

"Scotland's NHS is now performing better against tougher targets, and the level and quality of care provided to patients has contributed to people living longer along with continued advances in diagnosis, treatment and care.

"There is still much more work to be done and we'll continue to work closely with a range of key organisations like the BMA as we put in place the changes we need to ensure our NHS can go on delivering high quality care for generations to come."

Scottish Labour public services spokesman Dr Richard Simpson, a former GP, said: "This is a stark warning from one of the most senior clinicians in Scotland.

"Now more than ever we need a well-resourced health service free at the point of delivery based on patient need not the ability to pay.

"Under this SNP Government, and particularly since Shona Robison became Health Secretary, we've seen our NHS lurch from one crisis to the next.

"From the problems with delayed discharge to the chaos at the new Queen Elizabeth University Hospital in Glasgow, the NHS isn't secure in the SNP's hands.

"Dr Bennie is right to say that we cannot rely on the goodwill of already over worked NHS staff.

"Doctors, nurses and all those who work in our health service have dedicated their careers to caring for others, but we know from the NHS staff survey that only a third of them think they actually get the support they need to do their jobs."