The First Minister has been accused of "letting down" children in need of mental health treatment after figures showed some youngsters are waiting almost two years to access services.

Scottish Liberal Democrat leader Willie Rennie pointed to the statistics as he questioned Nicola Sturgeon on why targets for those children to be treated with 18 weeks were being missed.

The First Minister disputed Mr Rennie's portrayal of the situation and said the increasing demand for services shows the stigma surrounding mental health problems is diminishing.

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"I think this is one of the most serious issues we face as a society," the SNP leader told MSPs at Holyrood.

NHS figures recently obtained by the Liberal Democrats show that a youngster waited for 96 weeks for child and adolescent mental health service (CAMHS) treatment in NHS Tayside.

Another patient waited 91 weeks in Fife and a few children have waited more than 24 months in Lothian every year since 2013/14.

Raising the issue at First Minister's Questions, Mr Rennie said: "New figures show that children in Scotland can wait up to two years for mental health treatment.

"The Scottish Government promised they would receive treatment within 18 weeks. That promise has not been kept this year or last year.

"Why is the First Minister letting these children down?"

Ms Sturgeon told him it was an important issue but added: "I don't agree that with that characterisation".

She said the Scottish Government recognises there is more work to be done to make sure that all young people get the access to mental health services they need but pointed to "increasing investment" in mental health services and a growing number of clinicians working in the area.

Ms Sturgeon highlighted Government plans to invest an additional £150 million in mental health services.

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She told the chamber: "Of course, we are seeing a significant rise in demand for those services and while that puts pressure on services that we have a responsibility to meet, we should welcome that increase in demand to the extent that it shows young people are now more able to come forward because the stigma around mental health is decreasing."