Women and children held in detention centres in Libya are in immediate danger after being caught up in mass arrests, the UN warned on Tuesday.
Five unaccompanied children and at least 30 infants are among the most vulnerable being held in Tripoli.
Unicef said about 751 women and 255 children were among the thousands of migrants and asylum seekers caught up in the recent arrests.
“Migrant and refugee children in Libya continue to face grave child rights violations, including arbitrary detention,” said Cristina Brugiolo, the acting Unicef special representative to Libya.
“Children are held under devastating and inhumane conditions in these detention centres.
"We can assume the actual number of children held may be much higher as many boys are reportedly placed in cells with adult males.”
Libya is a launching point for human traffickers sending migrants and asylum seekers from Africa to Europe across the Mediterranean Sea.
Greece and Italy, on the northern shores of the Mediterranean, are attractive destinations inside the EU.
Libyan authorities were urged to protect all detained children and prevent them being separated from their parents, carers and families.
“Unicef stands ready with partners to provide technical support including alternative care arrangements for the detained children,” Ms Brugiolo said.
Detention centres have been receiving numbers far larger than their capacity, Unicef said. Libya's largest centre is holding more than 5,000 people, which is four times its official capacity.
Unicef called for the immediate release of all children in detention centres across Libya.
Two days ago, the UN said guards had shot and killed at least six people at a Libyan centre for migrants.
The number of migrants intercepted on their way to Europe by the Libyan coastguard has trebled compared with last year.
By the end of August, about 23,600 people had been stopped or rescued by the coastguard since January, compared with 7,800 in the first eight months of 2020.
The EU and Italy have provided support to the Libyan coastguard to reduce illegal migration to their shores.
Europe is trying to prevent a new migration crisis at its borders after earlier surges caused a political backlash.
Brussels is supporting a transitional government in Libya after a decade of chaos. More than 200,000 Libyans are estimated to be displaced in their own country.