Donald Trump has threatened to deploy soldiers to the border with Mexico and close it off to stop the "large caravans" of migrants from Central America coming to the US.
The US president tweeted: "I am watching the Democrat Party led (because they want Open Borders and existing weak laws) assault on our country by Guatemala, Honduras and El Salvador, whose leaders are doing little to stop this large flow of people, INCLUDING MANY CRIMINALS, from entering Mexico to U.S…..
"….In addition to stopping all payments to these countries, which seem to have almost no control over their population, I must, in the strongest of terms, ask Mexico to stop this onslaught – and if unable to do so I will call up the U.S. Military and CLOSE OUR SOUTHERN BORDER!..
"….The assault on our country at our Southern Border, including the Criminal elements and DRUGS pouring in, is far more important to me, as President, than Trade or the USMCA. Hopefully Mexico will stop this onslaught at their Northern Border. All Democrats fault for weak laws!"
According to reports in the US, one caravan fleeing Honduras is 4,000-strong.
Mr Trump has made cracking down on illegal immigration a keystone of his presidency and secretary of state Mike Pompeo is understood to be preparing to travel to Mexico for talks on stopping the influx of people.
The president's latest remarks come less than three weeks before the midterm elections and the Republicans are fighting to retain control of Congress.
Mr Pompeo's visit to Mexico comes ahead of the December inauguration of President-elect Andres Manuel Lopez Obrador.
Mr Trump had earlier this week threatened to withhold aid to the region as because of the caravan, as it travelled through Guatemala to Mexico in the hope of crossing into the US to escape violence and poverty.
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He tweeted on Tuesday: "The United States has strongly informed the President of Honduras that if the large Caravan of people heading to the U.S. is not stopped and brought back to Honduras, no more money or aid will be given to Honduras, effective immediately!"
Mr Trump returned to the issue on Thursday adding: "Hard to believe that with thousands of people from South of the Border, walking unimpeded toward our country in the form of large Caravans, that the Democrats won't approve legislation that will allow laws for the protection of our country. Great Midterm issue for Republicans!"