A Mexican law to severely limit the amount of dollars that banks can accept in cash has led drug cartels to bring money back to the U.S. to be deposited in American banks and wired back in pesos under the guise of international trade.

U.S. front companies for cartels aren't new, but U.S. officials say they took a more prominent role after Mexico's restrictions on dollar deposits were introduced in 2010. An Associated Press analysis of customs declarations shows San Diego became a magnet for cash coming to the country from Mexico.

Mexican President Enrique Pena Nieto lifted the restrictions last month, saying the anti-money laundering measure harmed honest businesses.