Thousands of children were probably illegally adopted abroad and brought to Switzerland between 1970 and 1990, the government admitted Friday.
The findings triggered ministers into seeking a revision of Switzerland's laws on adopting children from abroad.
Following numerous poignant testimonies from people illegally adopted in Sri Lanka, a first report in 2020 showed the authorities failed to take appropriate measures "despite early and clear indications" of irregularities in adoption placements.
The government commissioned a second study that was carried out by Zurich University of Applied Sciences (ZHAW) which looked at adoptions from 10 other countries: Bangladesh, Brazil, Chile, Colombia, Guatemala, India, Lebanon, Peru, Romania and South Korea.
"There were also indications of illegal practices, child trafficking, falsified documents and missing declarations of origin in these countries of origin," the government said in a statement.
"The number of entry permits issued suggests that several thousand adopted children could have been affected by irregularities during the period under investigation."
Over the period in question, ZHAW researchers found 8,000 authorisations for children to enter Switzerland, of which some 2,799 children came from India, 2,122 from Colombia, 1,222 from Brazil and 1,065 from South Korea.
The government "acknowledges the irregularities in international adoptions and regrets that the authorities did not adequately fulfil their responsibility towards the children and their families", it said.
"These shortcomings on the part of the authorities continue to shape the lives of adoptees to this day."
The federal government said it was up to the 26 cantons that make up Switzerland to support those affected in uncovering their origins.