More than 100 lawyers and politicians have written to the Norwegian Prime Minister to ask for the immediate release of children seized from the Christian Bodnariu family.

The letter is signed by attorneys from the US and around the world as well as several members of the European Parliament (MEPs). They say the decision to remove the five children was based on the family's Christian faith and was illegal.

"We find the facts of this international incident unacceptable not only on legal grounds but also on humanitarian and moral grounds. We view these transgressions as grievous breaches of domestic and international law," the letter read.

"Therefore, it is important that Norway immediately release the children back to their biological parents."

Last November Norway's state child protection service, known as the Barnevernet, removed the children. The parents, Ruth and Marius, have admitted spanking their children as punishment, which is illegal in Norway.

However it seems the decision to remove the children was also partly based on their Christian faith, according to the letter.

The signatories said they were "deeply disturbed" that the children's seizure was "motivated by the family's Christian faith".

It reads: "Barnevernet's own documents attest to the fact that the family's faith and religious values were at the core of the officials' discussions when debating the children's seizure."

The letter adds: "Barnevernet disapproved of the parenting style of the parents because, it concluded, it was 'based on the Bible."

The youngest of the children has now been returned but the others remain in custody with the parents allowed only sporadic, supervised contact.

The trial has sparked international protests with tens of thousands demanding the children be returned. Last month over fifty marches took place around the world with activists accusing the Barnevernet of removing the children without justification.