MEXICO CITY (Reuters) -Mexico's president on Monday hit back at U.S. criticism that her government was not doing enough to combat fentanyl, calling for the United States to do more to arrest drug traffickers on its own turf and stop the flow of weapons south across the border. The comments came after President Donald Trump threatened 30% tariffs against his southern neighbor and largest trading partner over the weekend, accusing Sheinbaum of failing to stop fentanyl being smuggled into the United States. "We do our part and they also have to do theirs," President Claudia Sheinbaum said at her regular morning press conference.