One day when Saburo Kita was 14, he was taken from an institution for troubled children to see a doctor. Despite protesting that his health was fine, he was ordered to strip, lie down on a table, and was given a local anaesthetic.

Then the surgery began.

He was left with a thick, v-shaped scar on his lower body and questions about what had happened. Months later, talking with a friend, he learned that he had been sterilised. So had two others from the same institution in Miyagi, northern Japan.

"There was no explanation, ever," said Kita, now 75, who uses the pseudonym in media to avoid questions from his late wife's family. "I was left with a body that couldn't create children."

But he did not realize until January that his surgery was part of a government programme to prevent the birth of so-called "inferior descendants" that saw tens of thousands sterilised, often without their consent, under a law not revoked until 1996.

Most were physically or cognitively disabled. But others suffered from leprosy - curable, and now known as Hansen's disease - mental illness or simply had behavioural problems. Kita had been sent to an institution for fighting at school.

Now the victims, many of whom were in their teens or younger when they were sterilised, are fighting back, demanding justice from a government they say violated their human rights. A mentally disabled woman in her 60s has sued for an apology and 11 million yen ($100,328) in compensation, and other suits may follow soon.

All could embarrass the government, which insists the surgeries were done legally, and Japan, where attitudes about the disabled still lag other advanced nations even as it prepares to host the Paralympic Games in 2020.

"Right after the war, rebuilding the country and its people was paramount, so in the name of building better citizens for the nation, the law came into effect," said Keiko Toshimitsu, a bioethics researcher and head of an activist group supporting those who were forcibly sterilised. "It was to build a better Japan - along, of course, with prejudice against the disabled.

"Then in the 1960s and 1970s there was rapid economic growth so they needed people born who could keep the growth going."

An official at the Health Ministry, who declined to be named due to the sensitivity of the issue, would not discuss the law or the lawsuits in detail.

"It was an operation that was carried out according to a law that was in force at the time, so we are contesting it with the stance that it is not a matter for compensation," he said.