President Donald Trump has on multiple occasions called on Congress to fund the US-Mexico border wall's construction in order to stop illegal migrants from flooding into the country.

In a Thursday tweet, President Donald Trump said that the US state of Arizona “is bracing for a massive surge” of migrants along a “non-walled” part of the southern border, and reiterated his call for Democrats to endorse funding for the protective wall.

Arizona, together with our Military and Border Patrol, is bracing for a massive surge at a NON-WALLED area. WE WILL NOT LET THEM THROUGH. Big danger. Nancy and Chuck must approve Boarder Security and the Wall! — Donald J. Trump (@realDonaldTrump) 7 декабря 2018 г.

The tweet came shortly after US Border Patrol officers and military personnel took part in "readiness exercises'' along the border in the city of Nogales, Arizona.

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US Customs and Border Protection had earlier issued a statement suggesting that the exercises would be held in order to prepare personnel for an influx of Central American migrants at the border.

"The exercises were training in preparation to deal with the potential of large crowds and assaultive behaviour by caravan members. They included tactical operations with the use of role players and inert smoke to simulate real-world environments. This training will allow our officers to respond tactically should a situation arise", the agency's statement read.

Earlier this week, US Defence Secretary Jim Mattis approved plans to extend the deployment of active-duty troops at the Mexico border until 31 January at the request of the Department of Homeland Security.

The troops are spread across California, Arizona, and Texas.

In late November, a caravan of about 5,000 asylum-seeking migrants from Central American countries reached the Mexican cities of Tijuana and Mexicali near the southern US border where some of the migrants clashed with US Border Patrol agents, who used tear gas to disperse the stone-throwing crowd.

Trump earlier threatened to close down the whole border between the US and Mexico, also stating that there could be another government shutdown in December if a bipartisan agreement on the border security issue was not reached.