PHOENIX  Calling Mexican drug trafficking organizations “a national security threat,” Attorney General Eric H. Holder Jr. announced Wednesday that federal authorities had mounted their biggest assault against one of Mexico’s most powerful drug cartels.

More than 750 people nationwide have been arrested, tons of cocaine and marijuana have been seized and the distribution of drugs has been disrupted through a series of raids and arrests as part of an investigation begun under the Bush administration 21 months ago, Mr. Holder said.

The operation comes at a time of rising concern over Mexico’s drug violence and the reach of trafficking organizations into the United States. It has focused on the Sinaloa cartel and culminated with a wave of arrests, unsealed indictments and seizures on Tuesday and early Wednesday in California, Maryland and Minnesota.

The Sinaloa organization, based in Sinaloa State in northwest Mexico, is one of the oldest cartels and has been blamed for a large share of the spiraling violence in the country that has left more than 6,000 people dead in the past year amid turf wars and a government crackdown on their operations.