Key waiting-times targets are being missed by the NHS, according to official figures.

The health service failed to meet the 12-week treatment time guarantee during the quarter from April to June.

The guarantee established a 12-week maximum wait for planned treatment delivered on an inpatient or day case basis.

During the three-month period, 94.9 per cent of patients were seen within the treatment time guarantee.

A target for no patients to wait longer than 12 weeks for a new outpatient appointment at a consultant-led clinic was also missed.

At June 30, 89.7 per cent of new outpatients waiting for an appointment had been waiting 12 weeks or less.

In June, the health service also failed to meet its target to treat 90 per cent of patients within 18 weeks from the point they were referred by their doctor.

Across NHS Scotland, 88.3% of patients were reported as being seen within the target time, down from 91.1 per cent compared with the same period in the previous year.

Meanwhile, the latest A&E waiting-times figures show that 94.2 per cent of patients were seen and subsequently admitted, transferred or discharged with four hours during the week ending August 16 - missing the Scottish Government's interim target of 95 per cent.

Health Secretary Shona Robison said: "Weekly A&E performance continues to fluctuate, with today's figures showing 94.2 per cent of patients seen within four hours at core A&E sites.

"We have moved on considerably from when weekly reporting began in February, with performance during the week ending August 16 being 8.1 percentage points above that of the week ending February 22.

"However, I am clear that more needs to be done to continue to improve performance."

She added: "Our focus now is to maintain this improving trend in performance going forward - particularly as we head towards winter.

"We want to see long-term, sustainable change put in place in order to maintain this high level of performance during peaks and troughs of demand."

Ms Robison also highlighted improvements in A&E waiting times at the new Queen Elizabeth University Hospital in Glasgow.

A support team was sent in for two weeks in June after A&E performance fell to 78.6 per cent. Latest A&E performance at the hospital is 94.8 per cent.

"It is pleasing to see that the initial improvement in performance achieved during the support team's time at the hospital has continued in recent weeks, with performance at the Queen Elizabeth 16.2 percentage points higher than week ending June 14 when the support team arrived on site," Ms Robison said.

Commenting on the 12-week treatment time guarantee, she added: "Health boards across Scotland continue to deliver some of the lowest waiting times on record, with more than 875,000 patients treated within our 12-week treatment time guarantee since it was introduced in October 2012.

"However, more clearly needs to be done to maintain and improve on performance in order to meet the rightly demanding targets we have set. Patients should expect nothing less."

Ms Robison said a series of measures were being taken to reduce waiting times, including millions of pounds of targeted support and an outpatient delivery and improvement programme which will aim to "better the services outpatients receive and in turn improve waiting times".

Elsewhere, the waiting-times target for child and adolescent mental health (CAMH) services was also missed.

The Scottish Government set a target for a maximum wait of 26 weeks from a patient's referral to treatment for specialist CAMH services from March 2013, reducing to 18 weeks from December 2014.

The target should be delivered for at least 90% of patients.

New figures show that in the three months to the end of June, 85.2% of patients were seen within 26 weeks and 76.6% were seen within 18 weeks.

An 18-week treatment target for psychological therapies was only met by four health boards in the three months to the end of June.

Liberal Democrat MSP Jim Hume said: "SNP ministers must wake up to the growing pressure on mental health services.

"These figures are a national scandal given that one in four people will experience mental ill-health in their lifetime.

"Scottish Liberal Democrats urge the SNP government to enshrine parity in law between the treatment of mental and physical ill-health.

"This would be a starting block towards ensuring health boards have the resources they need to meet growing demand on mental health services."

Scottish Labour's public services spokesman Dr Richard Simpson said: "NHS staff work round the clock to provide the care Scots need but it is becoming increasingly clear that they are facing an uphill struggle because the SNP have squeezed health spending in Scotland harder than even the Tories in England. Today's statistics show our NHS under huge strain in a number of areas.

"It is very worrying to see continual missed targets in child mental health services. Having worked as a psychiatrist for over 20 years I know that delays to treatment only aggravate stress and can worsen a child's condition."

Jamie Hepburn, minister for sport, health improvement and mental health, said: "Waiting times for mental health treatments have come down significantly in recent years despite a large increase in demand.

"However, having become the first country in the UK to set waiting-times targets in this area, we are absolutely determined to maintain that improvement and reach the targets we have set.

"We have already invested a significant amount in mental health services, leading to record levels of specialists. In the last six years, Scotland's CAMHS workforce has increased by more than a quarter.

"There has been a significant increase in demand in recent years and an increasing number of young people starting treatment over the last two years. This is thought to be mainly because more people are seeking help.

"The £100 million fund we announced earlier this year will be key when it comes to making the further improvements we need."

Royal College of Nursing Scotland director Theresa Fyffe called for a review of NHS targets.

She said: "Targets are all well and good and have delivered some real improvements, but many of these targets, we believe, are now creating an unsustainable culture which often skews clinical priorities, wastes resources and focuses the energy of too many people in the health service on the wrong things."