Treasury Secretary Janet Yellen on Wednesday announced economic sanctions against 15 people and two companies that the United States says are linked to a Mexican drug cartel as she visited Mexico City for talks with officials about efforts to fight fentanyl trafficking. "We cannot end the U.S. opioid crisis and achieve greater security without looking beyond our borders," she said. Yellen traveled to Mexico this week after the Treasury Department announced a strike force to help combat illicit fentanyl trafficking as the U.S. and China step up efforts to stop the movement of the powerful opioid and drug-making materials into the U.S. When President Joe Biden and Chinese leader Xi Jinping met in California in November, they announced that China would instruct chemical companies to curtail shipments of the materials used to produce fentanyl to Latin America.