Between 30,000 to 50,000 Norwegians, labelled "German girls", had intimate relations with occupying troops during World War II, according to conservative estimates from Norway's Centre for Holocaust and Minorities Studies.
Many of these woman were subject to reprisals by officials after the 1945 liberation from Nazi occupation, including illegal arrests and detentions, job dismissals and even being stripped of their nationality.
"Young Norwegian girls and woman who had relations with German soldiers or were suspected of having them, were victims of undignified treatment," Norway's Prime Minister Erna Solberg said.
"Today, in the name of the government, I want to offer my apologies," the premier said at an event to mark the 70th anniversary of the UN's universal declaration of human rights.
More than 70 years after the end of WWII, very few of the women remain alive and the official apology is unlikely to open the way for financial reparations for their families.
During the war, more than 300,000 German soldiers occupied Norway, a neutral country the Nazis invaded on April 9, 1940.
"We cannot say women who had personal relations with German soldiers were helping the German war effort," said historian Guri Hjeltnes, the director of the Holocaust and Minorities Studies centre.
"Their crime was breaking unwritten rules and moral standards," Hjeltnes said. "They were punished even more harshly than the war profiteers."
None of the estimated 28 Norwegian men married to German women during the war were expelled or had their nationality taken away from them, the historian said.
In 2000, Olso formally apologised to the 10,000 to 12,000 children born to Norwegian mothers and German soldiers, who also suffered reprisals.