President Trump says he will close the US border with Mexico "entirely" if the "obstructionist Democrats" continue to oppose funding for the wall he wants to build between the two countries.
In a series of angry tweets, he also criticised the "ridiculous immigration laws that our country is saddled with" and wrote that "Honduras, Guatemala and El Salvador are doing nothing for the United States but taking our money".
In addition, he floated the idea of withdrawing from NAFTA, an agreement which led to free trade between the US, Canada and Mexico.
"Bring our car industry back into the United States where it belongs," he said.
"Go back to pre-NAFTA, before so many of our companies and jobs were so foolishly sent to Mexico. Either we build (finish) the wall or we close the border."
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He tweeted: "We will be forced to close the southern border entirely if the obstructionist Democrats do not give us the money to finish the wall and also change the ridiculous immigration laws that our country is saddled with.
"Hard to believe there was a congress and president who would approve!"
Mr Trump is seeking $5bn (£4bn) for the wall as the attempts to stop what he calls Mexican "murderers" and "rapists" coming into the country.
But opponents – mainly Democrats, and also some in his own Republican Party – say that building a barrier along the 2,000 mile border is impractical, and are refusing to grant funding.
The president claims, however, that closing the southern border would be a "profit making operation".
He wrote: "The United States loses so much money on trade with Mexico under NAFTA, over 75 billion dollars a year (not including drug money which would be many times that amount)."
He has retaliated against those opposing the wall by refusing to sign off a spending bill, leaving about 800,000 federal employees without pay and resulting in a partial government shutdown.
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In his tweets, the president also referred to groups of several hundred people, known as caravans, which have been walking north through south America to try to reach the US.
In his final tweet in a series of four, Mr Trump attacked the countries from which some of the people are travelling.
He wrote: "Honduras, Guatemala and El Salvador are doing nothing for the United States but taking our money.
"Word is that a new caravan is forming in Honduras and they are doing nothing about it.
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"We will be cutting off all aid to these three countries – taking advantage of US for years!"
American assistance has been given to the impoverished countries to try to improve democracy, human rights, education and security.
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Sky News
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