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WASHINGTON (AP) — President Donald Trump on Friday threatened to close America’s southern border or large sections of it next week, a potentially drastic step affecting the economies of both the U.S. and Mexico, if Mexico does not halt illegal immigration “immediately.”

“It could mean all trade” with Mexico, Trump said when questioned by reporters in Florida. “We will close it for a long time. I am not kidding around.”

Trump has previously threatened to close the border — including at a rally in Grand Rapids, Michigan, Thursday night — but this time was different as he gave a timetable. The White House did not immediately respond to questions about whether his possible action would apply to commercial and air travel, but a substantial closure could have an especially heavy impact on cross-border communities from San Diego to South Texas, as well as supermarkets, factories, and other businesses across the country that rely on trade from Mexico.

“If Mexico doesn’t immediately stop ALL illegal immigration coming into the United States through our Southern Border, I will be CLOSING the Border, or large sections of the Border, next week,” Trump said in a tweet. “This would be so easy for Mexico to do, but they just take our money and ‘talk.’”

Trump’s declaration came a day after Mexican President Andres Manuel Lopez Obrador said his country was doing its part to fight migrant smuggling. Criminal networks charge thousands of dollars a person to move migrants through Mexico, increasingly toward remote sections of the U.S.-Mexico border in large groups.

“We are going to do everything we can to help,” Lopez Obrador said. “We don’t in any way want a confrontation with the U.S. government.”

A senior Homeland Security official on Friday suggested Trump was referring to the ongoing surge of mostly Central American families crossing the border from Mexico. Many people who cross the border illegally ultimately request asylum under U.S. law, which does not require asylum seekers to enter at an official crossing.

The official said the U.S. might close designated ports of entry to re-deploy staff to help process parents and children.

Ports of entry are official crossing points that are used by residents and commercial vehicles. The official, who spoke to reporters on condition of anonymity, did not specify which ports the administration was considering closing, but said only that closures were “on the table.”

Customs and Border Protection commissioner Kevin McAleenan said Wednesday that 750 border inspectors would be reassigned to deal with the growing number of migrant families, and the DHS official said Friday that the department was seeking volunteers from other agencies to help.

Democratic and Republican lawmakers have fought over whether there actually is a “crisis” at the border, particularly amid Trump’s push for a border wall, which he claims will solve immigration problems, though a wall wouldn’t keep out families who cross the border at official points so they can surrender and be detained.

The president called on Congress to immediately change what he said were weak U.S. immigration laws, which he blamed on Democrats. The Department of Homeland Security wants the authority to detain families for longer and more quickly deport children from Central America who arrive at the border on their own. The department argues those policy changes would stop families from trying to enter the U.S.