Mexican President Enrique Pena Nieto on Thursday cancelled a planned Jan. 31 meeting with President Donald J. Trump, hours after Trump tweeted that the meeting should be scrapped if Mexico won't pay for a border wall.

Pena Nieto's message on Twitter ended days of uncertainty about how he would respond to Trump's aggressive stance toward the country, and illustrated the challenges world leaders are likely to face in dealing with Trump's voluble, Twitter-based diplomacy.

 

It also signalled a remarkable souring of relations between the U.S. and its immediate southern neighbour, one of America's largest trading partners and a country with which it shares a nearly 2,000-mile border.

"This morning we have informed the White House I will not attend the working meeting planned for next Tuesday," Pena Nieto tweeted.

"Mexico reaffirms its willingness to work with the United States to reach agreements that benefit both nations," he added.

White House press secretary Sean Spicer responded to the Mexican president's announcement, saying: "We'll look for a date to schedule something in the future. We will keep the lines of communication open."

Earlier Thursday, Trump had tweeted that "If Mexico is unwilling to pay for the badly needed wall, then it would be better to cancel the upcoming meeting" in Washington D.C.

Trump said Wednesday he would start building a U.S.-Mexico border wall and has vowed to make Mexico pay for it. Mexico opposes the wall and has repeatedly said it won't pay.

DIPLOMACY VIA TWITTER

Officials had said Mexico was "considering" cancelling after the border wall announcement, but Trump appeared to beat Mexico to the punch in that game of brinkmanship.

Former foreign relations secretary Jorge Castaneda told local media that after Trump's tweet, "Pena Nieto has no other choice but to say 'I'm not going."'

Trump's unpredictable style appeared to catch Mexico's normally quiet and cautious diplomacy off guard.

"I think that, in general, diplomacy is not conducted via Twitter," Finance Secretary Jose Antonio Meade told Radio Formula.

Mexico's best-known opposition politician, leftist Andres Manuel Lopez Obrador, tweeted that "in the face of Trump's latest outburst, don't go to the meeting, and submit an urgent complaint to the U.N. for human rights violations."

$12-15 BILLION WALL?

House Speaker Paul Ryan says President Donald Trump's border wall will cost $12 billion to $15 billion -- and Ryan says Congress will pay for it by this fall.

The Wisconsin Republican made his comments to reporters in Philadelphia, where GOP lawmakers are holding their annual strategy retreat.

Ryan was pressed on whether the wall's price tag would be added to the deficit -- or whether Congress would find some ways to offset the cost. But he wouldn't commit.

The point, Ryan says, is that Congress will pay for "the construction of a physical barrier on the border."

WALL REPAYMENT PLAN

Trump wants to pay for his proposed southern border wall by slapping a 20 per cent tax on imports from Mexico.

Spicer says Trump has discussed the idea with congressional leaders and wants to include the measure in a comprehensive tax reform package.

The secretary spoke to reporters on Air Force One as Trump flew back from a Republican retreat in Philadelphia. He says that taxing imports from Mexico would generate $10 billion a year and "easily pay for the wall."

Spicer says discussions are continuing with lawmakers to make sure the plan is "done right." But he says it "clearly provides funding" for the wall.