By Chris Robertson, news reporter
The UN's high commissioner for human rights has said she is "appalled" by the conditions that migrants face at US border facilities.
Her comments intensify the challenge to President Donald Trump over his administration's immigration policies.
Michelle Bachelet said children stopped by border agents should never have to be held in detention facilities, or be separated from their families.
She also added that detention should not be the norm for adults either, saying: "Any deprivation of liberty of adult migrants and refugees should be a measure of last resort."
In a statement, Ms Bachelet said many migrants and refugees set off on "perilous journeys with their children in search of protection and dignity and away from violence and hunger".
"When they finally believe they have arrived in safety, they may find themselves separated from their loved ones and locked in undignified conditions," she said.
"This should never happen anywhere."
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The findings come after President Trump said at the weekend that migrants were "very happy with what's going on because, relatively speaking, they're in much better shape right now."
He also praised the work of border patrol agents on the Mexico-US border saying: "It's incredible what they're doing. They've had to become nurses. They've had to become janitors."
Ms Bachelet, a former president of Chile, added: "As a paediatrician, but also as a mother and a former head of state, I am deeply shocked that children are forced to sleep on the floor in overcrowded facilities, without access to adequate healthcare or food, and with poor sanitation conditions.
"Detaining a child even for short periods under good conditions can have a serious impact on their health and development – consider the damage being done every day by allowing this alarming situation to continue."