This story has been updated from when it was first published at 12:45 p.m. to include comments from President Trump in Philadelphia.

Mexican President Enrique Pena Nieto called off his meeting with U.S. President Donald Trump, sending the Mexican peso lower amid growing uncertainty about the future of the relationship between the two North American countries.

Pena Nieto said on Twitter Thursday that his administration has informed the White House that he will not attend the meeting planned for January 31 with Trump. The announcement came just a few hours after Trump tweeted that the meeting should be cancelled if Mexico was unwilling to pay for a wall at the U.S.-Mexico border, for which he signed an executive order on Wednesday.

The Mexican peso, which has been the hardest-hit currency since Trump's election, was down about 1% against the U.S. dollar midday Thursday. The Canadian dollar -- the currency of the third leg of the North American Free Trade Agreement Trump says he wants to renegotiate -- fell about 0.30%.

The iShares MSCI Mexico Capped Index ETF (EWW - Get Report) , which tracks stocks traded on the Mexican stock exchange, was down about 2.25%. The ProShares Ultra MSCI Mexico Capped IMI ETF (UMX) that tracks the Mexican equity market fell more than 5%.

Shares of Cemex  (CX - Get Report) , the Mexican cement company some have speculated could benefit from Trump's wall, fell 3.3%.

Trump reacted to the cancellation while addressing congressional Republicans in Philadelphia on Thursday.

"Unless Mexico is going to treat the United States fairly, with respect, such a meeting would be fruitless, and I want to go a different route," he said.

Both leaders' tones made a significant shift in just a 24-hour period. On Wednesday, Pena Nieto and Trump appeared hopeful about the future of relations between their countries.

Pena Nieto in a tweet on Wednesday reaffirmed Mexico's "friendship" with the American people and willingness to reach agreements with the U.S. government. He also reiterated the country's willingness to work with the U.S. to reach agreements that favor both nations.

Trump said in an interview Wednesday with ABC News' David Muir that he wants a "very stable, very solid Mexico" and thinks "the relationship [between the two countries] will be better than ever before."

Pena Nieto and other Mexican leaders have remained defiant that Mexico will not pay or reimburse the United States for Trump's proposed wall at the border, which may cost as much as $15 billion.

He reiterated the stance in a video address delivered Wednesday evening. "Mexico does not believe in walls. I have said time and time again, Mexico will not pay for the wall," he said.

"He has to say that," Trump said when asked by Muir about Pena Nieto's insistence Mexico will not pay. "But I'm just telling you there will be a payment."

Mexico has been bracing for Trump's inauguration for quite some time, and there were hopes that the administration's new foreign minister, Luis Videgaray, would help ease relations between the two countries given his ties to those close to Trump. Videgaray and Mexican economy minister Ildefonso Guajardo are in Washington this week laying the groundwork for next week's now-cancelled meeting.