The UN children's agency said on Thursday that hundreds of children and teens rescued by Malaysian authorities from care homes where they were allegedly physically and sexually abused faced an "unimaginable horror".
"These children have experienced unimaginable horrors and will need long-term professional medical and psychosocial support," Robert Gass, the Malaysia representative for UNICEF, said.
"The damage caused is serious and often results in lifelong consequences."
Large-scale raids were carried out by authorities on Wednesday at charity homes across two states.
Initial investigations revealed the victims were sexually abused by their caretakers and forced to abuse other children, the police said Wednesday.
The raids led to some 170 arrests, including Islamic religious teachers and caretakers at the welfare homes, according to police.
Police have said the homes were run by an Islamic business organisation with links to a banned sect.
Global Ikhwan Services and Business (GISB) has been linked to Al-Arqam, an Islamic sect that was banned by the authorities in 1994.
GISB has denied any wrongdoing and said in a statement it did not manage the homes.
"It is not our policy to do things that go against Islam and the laws," the firm said in a statement Wednesday.
According to its website, GISB runs various businesses such as supermarkets and restaurants, and operates in several countries including Indonesia, France and the United Kingdom.
Police have said the children would be temporarily housed at a police training centre in the capital Kuala Lumpur.