Project Southbound targeted the Surenos, also known as Sur 13, a transnational gang with roots in southern California implicated in murder, extortion, drug trafficking, prostitution and other crimes.
Among those arrested was a 27-year-old in Texas wanted for murder in his native El Salvador and a San Francisco man accused of supplying large quantities of premium marijuana to Surenos members.
The Department of Justice has called the Surenos the fastest-growing gang in the United States on a national level.
"This gang now has more than 30,000 members in the United States and its numbers are growing," he said, adding that ICE would "continue to disrupt and dismantle" its activities.
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Besides the 638 gang members and associates, Project Southbound -- conducted with help from federal, state and local law enforcement agencies -- netted 119 others wanted for various criminal and immigration offences.