PALM BEACH, Fla. (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 that sell Mexican produce, factories that rely on imported parts, and other businesses across the country.

The U.S. and Mexico trade about $1.7 billion in goods daily, according to the U.S. Chamber of Commerce, which said closing the border would be "an unmitigated economic debacle" that would threaten 5 million U.S. jobs.

"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 tweeted. "This would be so easy for Mexico to do, but they just take our money and 'talk.'"

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."

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 in large groups toward remote sections of the border.

"We want to have a good relationship with the government of the United States," Lopez Obrador said Friday. He added: "We are going to continue helping so that the migratory flow, those who pass through our country, do so according to the law, in an orderly way."

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.

Alejandra Mier y Teran, executive director of the Otay Mesa Chamber of Commerce in San Diego, said the mere threat of border closures sends the wrong message to businesses in Mexico and may eventually scare companies into turning to Asia for their supply chains.

"I think the impact would be absolutely devastating on so many fronts," said Mier y Teran, whose members rely on the Otay Mesa crossing to bring televisions, medical devices and a wide range of products to the U.S. "In terms of a long-term effect, it's basically shooting yourself in your foot. It's sending out a message to other countries that, 'Don't come because our borders may not work at any time.' That is extremely scary and dangerous."

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Nomaan Merchant reported from Houston, Catherine Lucey from Washington. Associated Press writers Peter Orsi in Mexico City and Elliot Spagat in San Diego contributed to this report.

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