President Donald Trump on Saturday threatened to impose a 30% tariff on key US trading partners Mexico and the European Union, ramping up pressure for deals in his trade wars.

Both sets of duties would take effect August 1, Trump said in separate letters posted to his Truth Social platform, citing Mexico's role in illicit drugs flowing into the United States and a trade imbalance with the EU, respectively.

This development came after weeks of negotiations with the key trading allies failed to reach a more comprehensive trade deal.

Earlier this week, Trump issued new tariff announcements for a number of countries, including Japan, South Korea, Canada and Brazil, as well as a 50% tariff on copper.

Mexico slammed US President Donald Trump's latest threat of 30% tariffs Saturday as an "unfair deal," according to a government statement.

Mexico was informed of the new duties — which Trump said would come into effect by August 1 — during talks in the United States on Friday.

"We mentioned at the table that it was an unfair deal and that we did not agree," the Mexican economy and foreign ministries said in a joint statement.

In response to the US move, European Council President Antonio Costa said that the EU remains in full support of efforts to reach fair agreement with US.

"EU will continue to build strong trade partnerships worldwide," said President Costa, adding that free and fair trade drives prosperity, creates jobs and strengthens supply chains.

The EU had hoped to reach a comprehensive trade agreement with the US for the 27-country bloc.

The European Union had been bracing for the letter from Trump outlining his planned duties on the United States' largest trade and investment partner after a broadening of his tariff war in recent days.

The EU initially hoped to strike a comprehensive trade agreement, including zero-for-zero tariffs on industrial goods, but months of difficult talks have led to the realization it will probably have to settle for an interim agreement and hope something better can still be negotiated.

The 27-country bloc is under conflicting pressures as powerhouse Germany urged a quick deal to safeguard its industry, while other EU members, such as France, have said EU negotiators should not cave into a one-sided deal on US terms.

Trump's cascade of tariff orders since returning to the White House has begun generating tens of billions of dollars a month in new revenue for the US government. U.S. customs duties revenue shot past $100 billion in the federal fiscal year through to June, according to U.S. Treasury data on Friday.