Norway's Prime Minister Erna Solberg has issued an official government apology to Norwegian women who were mistreated over World War Two-era relationships with German soldiers.

Norway, a neutral country, was invaded by Nazi forces in April 1940.

Up to 50,000 Norwegian women are thought to have had intimate relationships with German soldiers.

The Germans were also encouraged to have children with them by SS leader Heinrich Himmler.

Himmler, one of the most powerful men under Adolf Hitler, favoured Norwegian women, hoping they could help promote the Nazi concept of an Aryan master race.

Many of the Norwegian-German children were born in the German-administered Lebensborn (Fountain of Life) maternity facilities set up from 1941 by the Nazis in the country.

The women who had relationships with the soldiers became known by the nickname the "German Girls", and were targeted for reprisals in Norway when the war ended - standing accused of betraying the country.

Punishments included being deprived of civil rights, detained or expelled from the country to Germany along with their children.

'Undignified treatment'
"Young Norwegian girls and women who had relations with German soldiers or were suspected of having them, were victims of undignified treatment," Ms Solberg said at an event to mark the 70th anniversary of the UN's Universal Declaration of Human Rights on Wednesday.

"Our conclusion is that Norwegian authorities violated the rule fundamental principle that no citizen can be punished without trial or sentenced without law."

"For many, this was just a teenage love, for some, the love of their lives with an enemy soldier or an innocent flirt that left its mark for the rest of their lives.

"Today, in the name of the government, I want to offer my apologies."

The apology was based on a report about Norway's post-war actions published by the country's Centre for Holocaust and Minorities Studies.

More than seven decades on from the war, not many of the women directly affected are likely to still be alive to hear it.

"A good apology can have a lot of power. An apology can mean that groups receive answers to their treatment," Guri Hjeltnes the head of the centre said.

Reidar Gabler attended the event and told Norwegian media that the apology meant a lot to his family.

His mother, Else Huth from Sarpsborg was just 22 in 1944 when she fell in love with a 25-year-old German soldier.

"The people directly affected are no longer with us... but this also touches their families and the children," said Mr Gabler.

"We just had to come. This is amazing," he said, after meeting Ms Solberg.

About 10-12,000 children are thought to have been born as a result of relationships between Norwegian women and German soldiers.

Some of the children were also targeted for acts of revenge, given up to foster families or placed in institutions.

In 2007 a group of children took Norway to the European Court of Human Rights, but their case was ruled inadmissible because of the amount of time that had passed since the offences occurred.