GENEVA (AP) — An independent expert working with the U.N. human rights office estimates that over 100,000 children are being held in migration-related detention in the United States.

Human rights lawyer Manfred Nowak said Monday the U.S. is holding “far more” than are other countries for which he has reliable figures. About 60 out of every 100,000 children in the U.S. are deprived of liberty, versus about five on average in Western Europe.

Nowak said country-specific figures for the U.N. Global Study on Children Deprived of Liberty, a version of which was released in July, will be published Tuesday. Data came from government and advocacy group statistics.

The U.S. government didn’t respond to his team’s questionnaire. The U.S. is the only country not to have ratified the Convention on the Rights of the Child.