Mexican security forces have detained about 475,000 irregular migrants since October, authorities said on Friday, as US President-elect Donald Trump threatens Mexico with tariffs unless it stops illegal migrants from arriving at the shared border.

Nearly half a million migrants being detained between Oct. 1 and Dec. 26 suggests measures intensified towards the end of the year.

Since the start of the year, some 900,000 migrants have been detained, the government said earlier this month.

“We think it’s a model that works, that can always be improved, but that has responded very satisfactorily to this (migration) phenomenon,” Foreign Minister Juan Ramon de la Fuente said on Friday.

Speaking alongside President Claudia Sheinbaum at her regular press conference, he said the number of migrants detained at the shared border fell 81% in mid-December when compared to a year earlier.

Israel Ibarra, a researcher on immigration issues at the Colegio de la Frontera Norte, said the increase in detentions was in part due to “the commitment to reduce the transit of people in mobility through Mexico and to the United States” made by Sheinbaum in a recent call with Trump.

The call between Sheinbaum and Trump took place in late November after the Republican threatened to impose a 25% tariff on imports from Mexico and Canada if those countries do not stop the arrival of drugs, mostly fentanyl, and migrants.