Federal agents announced Tuesday they had arrested 678 alleged gang members in 168 cities as part of a nationwide crackdown on Mexican drug cartels. Officials said around two-thirds of those arrested were foreign nationals, and nearly half have ties to drug-trafficking groups, mainly in Mexico. The Department of Homeland Security’s Immigration and Customs unit said they were related to 113 different gangs and 13 were linked to Mexican drug cartels. The arrests came only a day before Mexican President Felipe Calderón is scheduled to visit the U.S., and two weeks after a U.S. agent was shot dead in Mexico, the first such killing in 25 years. Nearly 35,000 people have been killed in the Mexican drug war since 2006, when Calderon deployed troops and federal police to crack down on organized crime.