Republican senators have voiced “deep concern” about Donald Trump’s threat to impose tariffs on all goods imported from Mexico in a rare clash with the US president.

But Mr Trump said his party colleagues would be “foolish” to try to stop him going ahead within the plan, and it is unclear if they will be able to block it.

Mexican officials, who will meet US government negotiators in Washington, remain hopeful that high-level talks will ease the president away from his threat.

But with the 5 per cent tariffs set to start on Monday — and Mr Trump declaring them “more likely” than not to take effect — congressional Republicans warned the White House they are ready to stand up to the president.

The public split and looming standoff has revealed a fundamental difference in values between the president and his party.

Mr Trump uses tariffs as leverage to get what he wants – in this case to force Mexico to do more to stop illegal immigration. But tariffs are counter to firmly rooted Republican ideology and viewed by many in the party as little more more than taxes.

Senate majority leader Mitch McConnell said on Tuesday: “There is not much support in my conference for tariffs, that’s for sure.”

At a lengthy closed-doors lunch meeting on Capitol Hill, senators took turns warning Mr Trump’s officials there could be trouble if the Republican-held Senate votes against the Mexico tariffs.

Congressional rejection would be a stiff rebuke to the president, and even more forceful than an earlier effort to prevent him from shifting money to build his long-promised border wall with Mexico.

Texas senator Ted Cruz of Texas said the mood was one of “deep concern and resistance”.

“I will yield to nobody in passion and seriousness and commitment to securing the border, but there’s no reason for Texas farmers and ranchers and manufacturers and small businesses to pay the price of massive new taxes,” he added.

Ron Johnson, of Wisconsin, who was among the senators who spoke up in Tuesday’s meeting, said: “I think the administration has to be concerned about another vote of disapproval … I’m not the only one saying it.”

The outcome of such a vote would be uncertain, as Mr Trump could use a presidential veto to force through his plan.

But many Republicans who voted against the president earlier this year actually supported his ultimate goal of building the border wall, and were just uneasy with his executive reach to do it. On tariffs, Mr Trump has nowhere near the same backing.

The GOP opposition to the levies is grounded in fears over potential damage to the US economy. Senators worry they would spike US consumers’ costs and imperil a prospective major US-Mexico-Canada trade deal.

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The Mexican government is also concerned about the tariffs, but top officials seem optimistic about a resolution.

“By what we have seen so far, we will be able to reach an agreement,” foreign minister Marcelo Ebrard said during a news conference at the Mexican Embassy in Washington. “That is why I think the imposition of tariffs can be avoided.”

Mr Trump, during a press conference in London, offered mixed messages.

“We’re going to see if we can do something,” he said on the second day of his state visit to Britain. “But I think it’s more likely that the tariffs go on.”

He also said he doubted if Republicans in congress could muster the votes against him, adding: ”If they do, it’s foolish.”