"Mexico will never accept any action that violates our national sovereignty," Foreign Minister Marcelo Ebrard tweeted. "We will act firmly. I have sent our position to the U.S. as well as our resolution on combating transnational organized crime."
The Foreign Ministry said Ebrard would contact Secretary of State Mike Pompeo to set up an urgent meeting to discuss "this theme of high relevance for the bilateral agenda."
Trump told former Fox News host Bill O'Reilly in a radio interview broadcast Tuesday that Mexican cartels "will be designated" as Foreign Terrorist Organizations. The president noted that he had already suggested sending the U.S. military to help Mexico tackle organized crime, but was turned down by Mexican President Andr├ęs Manuel L├│pez Obrador.
"I've actually offered him to let us go in and clean it out and he so far has rejected the offer. But at some point, [something] has to be done," Trump said, citing the damage done by drugs to American addicts and their families.
The president added that the American government had been working on the terrorist designation for the past 90 days. "You have to go through a process, and we're well into that process," he said.
Under U.S. law, a violent foreign group or individual who threatens American security can be designated as terrorist in nature and be subject to special sanctions. Any institution dealing with a designated terrorist - such as a bank or government official - comes under heavy scrutiny and potential punishment.
Arturo Sarukhan, a former Mexican ambassador to Washington, said that the U.S. government could go so far as limiting cooperation with a country that is home to designated terrorist groups, reducing imports or refusing to vote for loans for that nation from multilateral organizations.
Presidents George W. Bush and Barack Obama had considered designating Mexican drug lords or cartels as terrorists, he said in a telephone interview. "When they realized the economic and trade implications it would have on U.S.-Mexican ties, they backed down."
A terrorist designation could also disrupt the bilateral cooperation in fighting organized crime built up over years, Sarukhan said.
The news is sure to revive Mexicans' concerns about possible U.S. military involvement in combating drug trafficking on their soil - a highly sensitive subject.
Mexico appeared to be caught off-guard by Trump's announcement. On Monday, Ebrard said Mexico "would never accept" that its criminal groups be designated as terrorists by the U.S. government, because "this invokes a disposition to act in a direct manner."
"But I think the United States isn't going to go this route," he said.
Mexico's homicide rate is on track to hit record levels this year, with organized-crime groups battling over trafficking routes, extortion rackets, gasoline theft and other activities in many parts of the country. The violence received new attention earlier this month, when suspected cartel members gunned down seven dual U.S.-Mexican citizens belonging to the extended LeBaron family, who were living in the northern state of Sonora.
Lopez Obrador, a leftist who took office a year ago, has maintained a generally cordial relationship with Trump, despite the U.S. leader's frequent criticism of Mexico. In June, the Mexican leader agreed to crack down on U.S.-bound migrants from Central America after Trump threatened stiff tariffs
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