Experts have gathered in Edinburgh for a major conference on childhood obesity.

The Scottish executive pledged to step up its efforts to tackle the problem on Tuesday in the light of new figures showing that one in five 12-year-olds north of the border is clinically obese.

Ministers set out a strategy earlier this year for improving children's diets and activity levels, which are among the worst in Europe.

But Holyrood deputy health minister Rhona Brankin said more must be done before the obesity-related diseases set in in later life.

"We cannot sit back and do nothing in the face of this health time bomb," she said.

"Scotland's children are our future and we must offer the building blocks that will help them make healthier choices.

"A lot of the work we are taking forward is based on education and raising awareness. I firmly believe this is the best approach.

"With comprehension comes informed choice and co-operation. Everyone has a part to play in encouraging children to become more active and eat more healthily."

However the SNP said the executive should set firmer targets for reducing obesity.

"We have already grasped the nettle in terms of smoking in public places and we must do the same to counteract our poor record on other areas of public health," health spokeswoman Shona Robison said.

"But while the executive has strong words on the matter, it has yet to even set a target for reducing obscenely high levels of obesity in Scotland," she added.