MEXICO CITY (Reuters) -Mexican President Claudia Sheinbaum on Saturday ordered retaliatory tariffs in response to the U.S. decision to slap 25% tariffs on all goods coming from Mexico, marking the apparent start of a trade war between the two countries.

In a lengthy post on X, Sheinbaum said her government sought dialogue rather than confrontation with its northern neighbor, but that Mexico had been forced to respond in kind.

"I've instructed my economy minister to implement the plan B we've been working on, which includes tariff and non-tariff measures in defense of Mexico's interests," Sheinbaum posted, without going into detail on what U.S. goods her government will target.

The United States is by far Mexico's most important foreign market, while Mexico in 2023 overtook China to become the top destination for U.S. exports.

Mexico has been preparing possible retaliatory tariffs against imports from the U.S., ranging from 5% to 20%, on pork, cheese, fresh produce, as well as manufactured steel and aluminum, according to sources familiar with the matter. The auto industry would initially be exempt, they said.

U.S. exports to Mexico accounted for more than $322 billion in 2023, Census Bureau data showed, while the U.S. imported more than $475 billion worth of Mexican products.

In her post, Sheinbaum also rejected as "slander" the allegation by the White House that drug cartels have an alliance with the Mexican government, a point used by the administration of President Donald Trump to explain why it had imposed the tariffs.

Trump said the tariffs against Mexico were due to the country's failure to stop fentanyl getting into the United States as well as what he describes as uncontrolled migration.

Sheinbaum also touted her government's record since she took office in October - seizing 20 million doses of deadly synthetic opioid fentanyl, in addition to detaining over 10,0000 individuals tied to drug trafficking.