The U.N. human rights office (UNHCR) is criticizing the United States’ new zero tolerance policy aimed at deterring migrants and refugees from coming to the country. Under this policy, people caught entering the U.S. irregularly are subject to criminal prosecution, and their children, some very young, are taken away.

The UNHCR calls this separation of family arbitrary and a serious violation of a child’s rights. The United States is the only country that has not ratified the U.N. Convention on the Rights of the Child. Nevertheless, the agency said this does not absolve the U.S. from its responsibilities to adhere to and protect these rights.

Human rights spokeswoman Ravina Shamdasani said the use of immigration detention and family separation as a deterrent runs counter to human rights standards and principles. She said children should never be detained because of their or their parents’ immigration status.

She told VOA there is no justification for detaining children.

“Detention is never in the best interest of the child and always constitutes a child rights violation,” she noted. “Entering a country without the relevant papers should not be a criminal offense. At most, it should be an administrative offense. So, these people should not be detained. Detention is never in the best interest of the child, and these children are effectively detained. They are separated and detained.”

The U.N. refugee agency also condemned the Trump administration’s immigration policy. It said preserving family unity is a fundamental tenet of refugee protection.

UNHCR spokesman William Spindler said the unity of the family is sacrosanct and should be preserved in the best interest of children and society as a whole. He said detention should be a measure of last resort.

“Most of the people attempting to enter the United States across the southern border are coming from three Central American countries: Guatemala, Honduras and El Salvador, which are experiencing high levels of violence and persecution, often targeting children and young people and forcing families to flee to protect their lives,” he said.

Spindler added that people fleeing countries of violence should be given international protection. He said the right to claim asylum is a fundamental human right.

U.S. Attorney General Jeff Sessions announced the “zero tolerance” policy several weeks ago. Sessions said Congress has failed to pass legislation to fix the problem. The issue has sparked a political debate in the U.S. ahead of midterm congressional elections later this year.