Fashion giant Zara is under investigation over the alleged use of slave labour at factories in Argentina.

Workers’ rights group La Alameda found immigrant workers, including children, producing clothes for the high street retailer in “degrading” sweatshop conditions, investigators said.

The labourers, mostly Bolivian, claimed they were made to work for more than 13 hours a day and were prevented from leaving the factory without permission.

Juan Gomez Centurion, head of the country’s health and safety watchdog, said: “We found men and children who lived in places where they worked. They were not registered and they were living in terrible conditions. They had no official documents and were held against their will, they were not allowed to leave their workplaces without permission.”

A Zara spokesman said: “We are surprised by the allegations. Based on the limited information we have received so far, the workshops in question do not appear to have any relationship with our approved suppliers in Argentina.”