U.S. President Donald Trump on Saturday threatened to impose 30 percent tariffs on imports from Mexico and the European Union starting August 1, after weeks of negotiations with the major U.S. trading partners failed to reach a comprehensive trade deal.

The new tariffs were announced in letters addressed to European Commission President Ursula von der Leyen and Mexican President Claudia Sheinbaum. The letters were posted on Trump's social media platform, Truth Social.

Trump criticized Mexico for its "failure to stop the cartels" from smuggling drugs, including fentanyl, into the United States, and accused the country of not doing enough to cooperate with Washington in curbing illegal immigration.

In the case of the EU, the U.S. president scolded the bloc for its tariff and non-tariff barriers, which he blamed for causing "long-term, large, and persistent Trade Deficits."

"Our relationship has been, unfortunately, far from reciprocal," he wrote in the letter to the EU.

Trump used largely the same wording in his letters as in those sent earlier this week to leaders of other countries, warning them not to retaliate, urging them to relocate companies to the United States, and suggesting that the tariff rates could be adjusted if they cooperate.

Trump has sent more than 20 similar letters to other U.S. trading partners in the past week, including Canada, South Korea, Japan and Brazil, with blanket tariff rates ranging from 20 percent to 50 percent.

Von der Leyen quickly responded to Trump's announcement, saying they are open to trade talks with the U.S. for an agreement before the deadline but won't rule out taking countermeasures.

"We remain ready to continue working towards an agreement by August 1," the EU leader said in a statement. "At the same time, we will take all necessary steps to safeguard EU interests, including the adoption of proportionate countermeasures if required."

"Imposing 30 percent tariffs on EU exports would disrupt essential transatlantic supply chains," she said. "We continue to deepen our global partnerships, firmly anchored in the principles of rules-based international trade."

Mexico's Ministry of Economy said Saturday it was informed the U.S. would send a letter during a meeting on Friday with U.S. officials. "We mentioned at the roundtable that it was unfair treatment and that we did not agree," the ministry's statement said, noting that the country is "already in negotiations with the U.S." to avoid the tariffs going into effect on August 1.

(With input from agencies)