WASHINGTON - President Donald Trump threatened on Friday to close the US border with Mexico next week, or at least large sections of it, if Mexico does not immediately stop illegal immigration into the United States.

Trump has repeatedly vowed to close the US border with Mexico during his two years in office, but this time the government is preparing to follow through as it struggles to deal with a surge of asylum seekers from countries in Central America, many of whom travel through Mexico to the border.

Department of Homeland Security officials warned that commerce with Mexico, the United States' third-largest trading partner, could slow down as the agency shifts 750 border personnel from ports of entry to help process asylum seekers who are turning up between official crossing points.

Nielsen and other US officials say border patrol officers have been overwhelmed by a dramatic increase in asylum seekers, many of them children and families, fleeing violence and economic hardship in El Salvador, Honduras and Guatemala.

Border patrol officers apprehended 66,450 people at the southern border in February, two and a half times the number they apprehended in February 2018.

It is not clear how shutting down ports of entry would deter asylum seekers, as they are legally able to request help as soon as they set foot on US soil.

But a border shutdown would disrupt tourism and commerce between the United States and Mexico, which totaled $612 billion last year, according to the US Census Bureau. Nielsen warned that the personnel shift would lead to commercial delays and longer wait times at crossing points.

Trump is trying to convince Congress to sign off on a revised trade agreement with Mexico and Canada that his administration negotiated last year.

Trump delivered his latest threat in a series of Twitter as at least hundreds of migrants were being held in a chain-link enclosure in El Paso, Texas, a border patrol official saying on Thursday that migrants were crossing at an average of 570 people per day in the area, the highest rate in more than a decade.

"Mexico has for many years made a fortune off of the US, far greater than Border Costs. 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," he wrote on Twitter.

Migrants illegally crossing the US border have led to tension between the United States and Mexico ever since Trump began his bid for the presidency almost four years ago, taking a hard line on immigration and saying Mexico was sending rapists and drug runners into the United States.

Mexican President Andres Manuel Lopez Obrador said on Thursday that tackling illegal immigration is an issue chiefly for the United States and the Central American countries to address.

Trump has so far been unable to convince Congress to tighten asylum laws or fund a proposed border wall that was one of the main platforms of his 2016 election campaign and then his presidency. Trump declared a "national emergency" in February to build the wall. Congress has not funded the wall and Trump has said he would use money earmarked for the military to pay for its construction.

Reuters