(Bloomberg) -- The US is stepping up efforts to keep drug money out of its financial system and stem the flood of fentanyl across its southern border, Treasury Secretary Janet Yellen said after a visit to a crime lab in Mexico City. 

Yellen announced sanctions against 15 individuals and two entities associated with the Beltran Leyva cartel, accused of smuggling the synthetic opioid, as well as cocaine and methamphetamine.

“US financial institutions are vulnerable, such as through exposure to drug trafficking organizations using shell companies,” Yellen said Wednesday. “These sanctions, alongside other recent designations, will help disrupt this behavior and undermine the broader dangerous network involved in the illicit supply and transfer of fentanyl. ”

Treasury analysts sift masses of financial transactions data to detect drug money flows, then threaten financial institutions with exclusion from the US banking system unless they cut off criminal actors. Even so, the US government has so far failed to significantly rein in the opioid epidemic, which Yellen said is killing more than 1,500 people per week. 

While in Mexico City this week, Yellen will meet President Andres Manuel Lopez Obrador, Finance Minister Rogelio Ramirez De La O, and members of the Mexican Bankers Association.

“Mexico’s been very helpful,” Yellen told reporters Tuesday, en route to the country’s capital. “We’re meeting with a number of the entities in Mexico that are providing us with information.”

Mexican banks, she added, have been “increasingly helpful in providing information that’s useful in tracing these flows.”

Read more: Mexico Joins Forces With China to Curb Illegal Chemicals Trade

Money Laundering

Some analysts are skeptical that financial sanctions will make a major impact on the flow of illegal drugs. Pressuring financial institutions is a necessary part of the fight against trafficking, but doesn’t strike at the roots of the problem, which include US demand, the drug’s immense profitability and the cartels’ dominance of swaths of Mexican society and law enforcement, said Falko Ernst, senior Mexico analyst at International Crisis Group.

“These measures have been very ineffective, making at best a partial dent into an ocean of problems and a money laundering structure that is very resilient,” he said.

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