UNHCR comments late Monday came after the Trump administration said it will end all asylum protections for most migrants who arrive at the U.S.-Mexico border.
The rule is expected to go into effect Tuesday and would affect many refugees fleeing violence and poverty in Central America. It is certain to face legal challenges.
According to the plan, migrants who pass through another country - in this case, Mexico - on their way to the United States will be ineligible for asylum.
UNHCR says the rule overly restricts the right to apply for asylum, and threatens the right not to be sent back to countries where people could face persecution.
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