US President-elect Donald Trump on Thursday said Mexico has agreed to immediately stop illegal immigrants from going to its border with the United States.

This comes days after Trump threatened to impose a 25 per cent tariff on all imports from Mexico and Canada for their inability to stop the flow of illegal immigrants into the United States.

In a post on his Truth Social platform, Trump said he spoke to Mexican President Claudia Sheinbaum Pardo on the phone and the two had a productive conversation.

"Mexico will stop people from going to our Southern Border, effective immediately. THIS WILL GO A LONG WAY TOWARD STOPPING THE ILLEGAL INVASION OF THE USA. Thank you," Trump said in his post.

"Just had a wonderful conversation with the new President of Mexico, Claudia Sheinbaum Pardo. She has agreed to stop Migration through Mexico, and into the United States, effectively closing our Southern Border," he said.

Trump said the two also talked about what could be done to stop the drug inflow into the United States and the consumption of these drugs.

"It was a very productive conversation," he added.

In a series of posts on his Truth Social platform on Monday, Trump said he would sign executive orders imposing a 25 tariff on imports from Canada and Mexico as one of his first actions after assuming office on January 20.

"As everyone is aware, thousands of people are pouring through Mexico and Canada, bringing Crime and Drugs at levels never seen before. Right now, a Caravan coming from Mexico, composed of thousands of people, seems to be unstoppable in its quest to come through our currently Open Border," Trump said.

"This Tariff will remain in effect until such time as Drugs, in particular Fentanyl, and all Illegal Aliens stop this Invasion of our Country! Both Mexico and Canada have the absolute right and power to easily solve this long simmering problem," he said.

On Thursday, the president-elect said he will be working on an advertising campaign to tell people how bad Fentanyl is.

"Millions of lives being so needlessly destroyed. By the time the campaign is over, everyone will know how really bad the horror of this drug is," he said.

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