By Matt Spetalnick

WASHINGTON The Biden administration is facing an "unwillingness" by Mexico to devote enough resources to help stem the flow of the illegal drug fentanyl into the United States, and is pressing Mexican authorities to do more, a U.S. official said on Thursday.

Todd Robinson, assistant secretary of state for international narcotics and law enforcement affairs, told a Senate subcommittee the U.S. was continuing to engage with the Mexican government "to convince them that they need to put more resources in" the fight against smuggling of the deadly opioid.

President Joe Biden's administration has been seeking increased cooperation from both Mexico and China in curbing the flow of fentanyl and its precursor chemicals, which have fueled a sharp rise in U.S. overdose deaths.

“To be honest, the challenge that we have with Mexico is their unwillingness to put … sufficient resources into the fight, and we are pushing them to do that,” Robinson said when asked whether Mexico was showing enough political will to tackle the fentanyl crisis.

“The partners that we are working with want to do more. They want to do better. They want to partner with us on greater security both in Mexico and at the border,” he said, adding that “we continue to engage with them on that.”

The Mexican embassy in Washington did not immediately respond to a request for comment.

Mexican Foreign Minister Alicia Barcena said on August 10 that Mexico was developing a digital tracking system for fentanyl precursor chemicals, including methods to detect the substances at Mexico's ports and border crossing points.

Mexico has vowed to crack down on precursors coming into the country, where they are used to produce fentanyl which is then often smuggled to the U.S.

Mexican President Andres Manuel Lopez Obrador, who has defended his country's efforts, said in April he had written to Chinese leader Xi Jinping urging him to help control shipments of fentanyl.

(Reporting By Matt Spetalnick; editing by Timothy Gardner)