US President Donald Trump paused tariffs on Mexico for one month after last-minute talks on Monday, but there was no breakthrough yet in negotiations with Canada on an issue that has sparked fears of a global trade war.

As world markets slumped, Trump and his Mexican counterpart Claudia Sheinbaum both announced the halt in the levies after she agreed to send 10,000 troops to the US-Mexico border following talks on Monday.

Trump said on his Truth Social network that after the "very friendly conversation" he had "agreed to immediately pause the anticipated tariffs for a one month period."

During that time there would be further talks "as we attempt to achieve a 'deal' between our two Countries," the Republican said.

Leftist Sheinbaum had announced the tariff pause a few minutes earlier, saying she had a "good conversation with President Trump with great respect for our relationship and sovereignty."

Trump agreed to increase measures to prevent trafficking of US weapons into Mexico, she said, a point that did not appear in Trump's statement.

The development came hours before the 25 percent levies that Trump has ordered on imports from the US neighbors and chief trading partners, plus an extra 10 percent on China, were due to take effect at midnight on Tuesday.

Trump said he had also spoken to Canadian Prime Minister Justin Trudeau on Monday and was due to speak again, but the White House said negotiations with Ottawa were not going as well.

Trump repeated his frequent claims that the United States is being unfairly treated by trade while pushing his argument that the tariffs were about a "drug war" from opioids "pouring through the Borders of Mexico and Canada."

US government figures show that only a minimal quantity of drugs comes via Canada. (AFP)