US President Donald Trump’s administration is pushing Mexican President Claudia Sheinbaum to do more to stop undocumented migrants from crossing the U.S. border after apprehensions reached the highest level of his second term.

Axar.az reports, citing Union Bulletin, that Secretary of State and National Security Adviser Marco Rubio delivered the message during a private meeting with Mexican Foreign Minister Roberto Velasco in Washington on Wednesday, according to people familiar with the matter, who asked not to be identified without permission to speak publicly.

The push is led by Homeland Security Adviser Stephen Miller, a top Trump adviser, and the main U.S. demand is that Mexico stop its own citizens from crossing the border, the people said. That presents a constitutional and legal complication for Sheinbaum’s government because Mexican nationals are free to travel within their own country, including from the poorer southern states where many migrants originate to northern Mexico and the U.S. border region.