President Donald Trump said he would probably close the US border if Mexico no longer prevents migrants from reaching the United States.
The closure would disrupt border crossings and jeopardize billions of dollars worth of trade.
Mr. Trump's threat follows an increase in migrants traveling through Mexico seeking asylum in the US.
Mexican President Andrés Manuel López Obrador said he would not face confrontation in this matter.
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Secretary of State Marcelo Ebrard said in a tweet that Mexico is a" big neighbor "of the US and" would not act on the basis of threats "
What did Mr. Trump say?
Mr. Trump told reporters Friday: "It's very likely that I'll close the border next week, and I'll be fine."
He said "It's very easy for Mexico to prevent people from coming but they do not opt for it."
The president later wrote a series of tweets that concluded that "because they lose so much money with them, especially if you add drug trafficking, etc., the US would be close to the border a good thing! "
The US President has also instructed the State Department to discontinue any direct assistance to El Salvador, Honduras and Guatemala, from which many migrants come.
The move must concern the Congress, from which many members have approved the grant of money the main causes of migration.
How did Mexico react?
President López Obrador said Thursday that migration was "not tied to us Mexicans".
He said it was a problem more likely to come from Central American countries than Mexico.
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"The Mexican is no longer seeking work in the United States. The majority [of migrants] are residents of our Central American compatriots," he said.
Following President Trump's tweets on Friday, Mr López Obrador told a crowd of followers: "I want to make it clear that we will not fight with the United States government – peace and love."
Migration as a "human right" and said, "The people of Central America have no options, so they start looking for a way to make a living."
Why does Trump want to close the border?
Homeland Security Secretary Kirstjen Nielsen said the border guard had been overwhelmed by a surge in asylum seekers who had fled violence in El Salvador, Honduras and Guatemala.
Department of Homeland Security (DHS) officials said that the March border arrests were expected to reach 100,000, the highest in a decade. More than 1,000 unaccompanied children are currently detained.
Ms. Nielsen warned Congress that the US government was facing a "system-wide collapse" when it tried to take care of the 6,600 immigrant families arrested.
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It is unclear how the closure of ports of entry could reduce the number of immigrants arriving as many arrive at unofficial entry points and can seek legal help as soon as they enter US soil.
The DHS has dispatched 750 border guards from the ports of entry to assist asylum seekers arriving between the official border crossings.
What could be the influence?
Ms Nielsen warned the Americans that they may "feel the effects of this plight".
Staff shortage is already having an effect. The traffic jams at the crossroads between Cuidad Juárez and El Paso, Texas, were longer than usual on Friday. One driver claimed to be stuck for three hours, Reuters reported.
Closing the border could have significant financial implications and disrupt tourism and trade between the US and Mexico, which reached US $ 612 billion last year, according to the US Census Bureau.
Kurt Honold CCE Business Group Leader in Tijuana, Mexico, said billions of dollars could be lost.
"It's obvious he does not measure what he says," Honold added.
What is the background to this?
President Trump's 2016 offer was based on a crackdown on illegal immigration, blaming Mexico for "bringing drugs, bringing crime to their rapists".
His famous promise to "build a wall" remains unfulfilled as Congress refuses funding. However, the president has declared a national emergency to direct the resources away from the military and against the wall.
Since his election in 2016, Mr. Trump has repeatedly threatened to close the US border with Mexico.
On Thursday, at a rally in Michigan, Mr. Trump told a group of fans that the US was closing the damn border. "[LIBERAL] On Friday, Mr López Obrador told reporters:" The whole talk of caravans with a migration background and such refers to politics and the election campaign [US]. Therefore, I will not respond. "