Sending thousands of older untested patients into care homes in England at the start of the coronavirus lockdown was a violation of their human rights, Amnesty International has said.
A report says government decisions were "inexplicable" and "disastrous", affecting mental and physical health.
More than 18,000 people living in care homes died with Covid-19 and Amnesty says the public inquiry promised by the government must begin immediately.
Ministers say they protected residents.
According to Amnesty's report, a "number of poor decisions at both the national and local levels had serious negative consequences for the health and lives of older people in care homes and resulted in the infringement of their human rights" as enshrined in law.
Researchers for the organisation interviewed relatives of older people who either died in care homes or are currently living in one; care home owners and staff, and legal and medical professionals.
Amnesty said it received reports of residents being denied GP and hospital NHS services during the pandemic, "violating their right to health and potentially their right to life, as well as their right to non-discrimination".
It adds that care home managers reported to its researchers that they were "pressured in different ways" to accept patients discharged from hospital who had not been tested or had Covid-19.
Amnesty says the public inquiry into the pandemic should begin with an "interim phase".
"The pandemic is not over," it added. "Lessons must be learned; remedial action must be taken without delay to ensure that mistakes are not repeated."
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In July, care homes in England were allowed to reopen again for family visits - as long as local authorities and public health teams said it was safe. That was followed by a similar reopening of homes in Scotland, Wales and Northern Ireland.
The report said regular testing needs to be made available for care home residents, staff and visitors to ensure visits can take place safely.
"Regular testing can help break the isolation that is so damaging to people's physical and mental health and could mean the difference between families being torn apart for months again," Amnesty said.
The report added that all the families interviewed whose relatives are currently in care homes said the current restrictions on visits - that there can only be one visitor per resident and no possibility of holding hands - made little sense.
They argue that staff can interact normally in the community and are only tested once a week at most, while having sustained physical contact with residents.
ORIGINAL ARTICLE: https://www.bbc.com/news/uk-54408723