Donald Trump has threatened to send the US military to close the Mexican border, in an angry early morning tweet attacking Democrats and a number of central American countries.

Returning to one of his common themes, the president’s string of posts falsely claimed the Democratic Party “want Open Borders [sic]”.

Without providing any evidence, he went on to allege an “assault on our country” by Guatemala, Honduras and El Salvador led by his political opponents and repeated a threat made earlier this week to cut off humanitarian aid.

“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,” he said.

“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!”

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Mr Trump’s rhetoric on immigration has been among the strongest – and most controversial – he has deployed so far in his presidency.

“These aren’t people, these are animals,” he said earlier this year of alleged gang members he said were entering the US illegally.

Today’s tweets were not the first time Mr Trump had suggested sending troops to the border with Mexico. In April he said he was “going to be doing things militarily” by sending the National Guard to help secure the area.

It echoed similar initiatives by both his immediate predecessors as president. George W Bush instituted Operation Jump Start from 2006 to 2008 in which 6,000 Guard troops were posted at the border, while Barack Obama’s administration sent some 1,200 from 2010 to 2011.

In July Mr Bush spoke out about what he called Mr Trump’s “disturbing” rhetoric. “It obscures the fact ... that the system is broken and needs to be fixed,” he said.

The latest outburst appeared to relate to a group reportedly numbering some 2,000 people making their way north from Honduras to the US border where they hope to seek refuge from endemic violence.

The so-called “march of the migrants” left the city of San Pedro Sula on Saturday despite pleas from authorities not to make the journey.

Honduran migrants sleep in Chiquimula, Guatemala, on 17 October (AFP/Getty Images)

“My husband was an electrician. They killed him nine months ago,” said Carolina Aguilar, 40, from the gang-controlled town of Choloma, sitting on a patch of ground with her two daughters aged 17 and 11.

“We don’t have a house and I have no job. We only manage to live from gifts,” she added in an interview at a migrant shelter in Guatemala City, Guatemala’s capital.

“We’ve lived in neighbourhoods where our children have seen disaster after disaster,” said Daisy Turcios, at an earlier stop on the road. “We have seen dead bodies thrown in front of us. So that’s my goal, in truth, to reach a country where life can change for my children.”

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Guatemalan president Jimmy Morales said on Wednesday that his government rejected constraints placed on foreign aid.

“No help can be conditioned and no help can be demanded,” he told reporters in the Guatemalan capital.

He said he had spoken with his Honduran counterpart, Juan Orlando Hernandez, about ensuring that those migrants who want to return home can do so safely, and cited reports indicating that many people from the caravan were returning to Honduras.

Luis Arreaga, the US ambassador to Guatemala, posted a video message on Twitter to migrants considering entering the US illegally.

“If you try to enter the United States, you will be detained and deported,” he said in Spanish. Addressing those already on their way, he added: “Return to your country. Your attempt to migrate will fail.”