MEXICO CITY — Thousands of Mexican National Guard members and other security forces are being deployed to the nation’s southern border with Guatemala this weekend, as the Mexican government seeks to make good on a deal struck with President Trump to reduce illegal migration.

The mobilization, which government officials say is a cornerstone of the deal with Washington that staved off potentially crushing tariffs, is expected to be complete by Tuesday. But the operation has been halting at best.

The new force had not been scheduled to begin formal operations around the country until the end of this month. “A lot of effort has been made to accelerate the pace,” Mexico’s foreign minister, Marcelo Ebrard, acknowledged on Friday.

And critics are worried that rushing the new Guard force into service, and into a job that was never meant to be its focus, could come at a great cost — for migrants and for Mexico.