Mexico slammed US President Donald Trump's latest threat of 30 percent 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 1 August — 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.

Mexico is already in negotiations seeking an alternative to tariffs that would protect businesses and jobs on both sides of the border, the ministries added, saying they hope to avoid the duties.

Mexico is one of the countries most vulnerable to the Republican leader's tariffs, with 80 percent of its exports destined for the United States, its largest trading partner. 

Since returning to the White House in January, Trump has reproached Mexico for not doing what he says is enough to prevent illegal migration and drug trafficking across the border, and has wielded tariffs as retaliation.