SYDNEY (AFP) - Australia on Thursday formally apologised for the forced adoption of tens of thousands of babies born mostly to unmarried mothers between the 1950s and 1970s.

The adoptions, driven largely by religious groups in the post-war period, "created a lifelong legacy of pain and suffering", the national apology delivered by Prime Minister Julia Gillard said.

"To you, the mothers who were betrayed by a system that gave you no choice and subjected you to manipulation, mistreatment and malpractice, we apologise," she said.

"We say sorry to you, the mothers who were denied knowledge of your rights, which meant you could not provide informed consent. You were given false assurances. You were forced to endure the coercion and brutality of practices that were unethical, dishonest and in many cases illegal."

The decision to offer a formal apology comes after a Senate inquiry into forced adoptions found as many as 225,000 babies were removed. Scores of mothers and children gave evidence at the inquiry, which looked at the forcible removal of infants between 1951 and 1975 in Australia, then a conservative and predominantly Christian nation.

Given the social stigma attached to unmarried females at the time, young women who fell pregnant were often sent to stay with relatives or at group houses run by churches or other religious organisations. Babies were often signed away for adoption before they were born. The inquiry found women were pressured to consent, signatures were sometimes fraudulently obtained, and adoption was presented as inevitable.

Women later struggled to reunite with their children. In many cases, adopted babies had their birth certificates issued in their adoptive parents' names, on the grounds that a "clean break" was best for all parties.