A 39-year-old woman and a 30-year-old man had been accused of physical and sexual violence over two years, from a very young age, against the two boys born of their union and the third boy from a previous relationship by the mother.

The boys now aged six, seven and 17 live with separate foster families.

The court in Øvre Romerike in southeast Norway based its guilty verdict on testimonies from the children given in some 20 hours of videos.

"Seeing the way the two little boys explain it, it is behaviour by their parents which they could not know and describe without having themselves been involved," said judge Karen Wendel Sandaa.

The boys said they were denied food, beaten and locked up nude in the basement, raped and made to abuse each other, in a room especially set up by their parents.

The couple moved the family 14 times to avoid being found out but social services finally intervened in 2011 after having been alerted about a possible case of abuse.

The two youngest boys were then placed in foster homes and talked about their ordeal.

The parents pleaded innocent to the charges saying the case was based on fabrications and misunderstandings. They have appealed the verdict.

"The prosecutor has called this case the most serious sexual abuse case ever examined by a Norwegian court. The court agrees," it said in its verdict.

Both parents were also ordered to pay 450,000 kroner (€60,000) to each of the three children.