Trump said 30% tariffs on the European Union and Mexico will take effect Aug. 1.

Stocks were mixed in early trading on Monday after President Donald Trump over the weekend issued 30% tariffs on the European Union and Mexico, rekindling tensions with two of the largest U.S. trade partners and threatening to raise consumer prices.

The Dow Jones Industrial Average dropped 115 points, or 0.26%, while the S&P 500 dropped 0.15%. The tech-heavy Nasdaq ticked up 0.04%.

Trump on Saturday announced new tariffs on the European Union and Mexico that will take effect on Aug. 1. That start date matches the onset of levies issued for more than 20 other countries in recent days, including top trade partners Canada, Japan and South Korea.

In a letter posted on his social media platform, Trump faulted Mexico for its alleged failure to stop the transport of fentanyl into the U.S. Between September and April, nearly all fentanyl seized by the U.S. came through the southern border with Mexico, according to U.S. Customs and Border Patrol, or CBP.

In response to a previous set of tariffs issued in February, Mexico vowed to take steps to address the transport of fentanyl, prompting Trump to temporarily pause the levies.

In a statement posted on X, Mexican economic minister Marcelo Ebrard said Mexico had already been negotiating with the U.S. to "protect businesses and jobs."

"We were informed that, as part of the profound changes in U.S. trade policy, all countries will receive a letter signed by the President of the United States establishing new tariffs starting August 1st," Ebrard said. "We stated at the meeting that this was an unfair deal and that we did not agree with it."

Trump sharply criticized the EU in a separate letter posted on social media, claiming the the U.S. runs an unacceptably high trade deficit with the EU. In a statement released on Saturday afternoon, European Commission President Ursula von der Leyen said the EU remains committed to "dialogue, stability, and a constructive transatlantic partnership."

ABC News' Kelsey Walsh and Patricio Chile contributed to this report.