WASHINGTON — Federal, state and local authorities across the country are sending an unequivocal message to Mexican drug cartel members in the U.S. and Latin America: If you kill a U.S. agent, there will be repercussions.

"This is personal," Louie Garcia, deputy special agent with the Immigration and Customs Enforcement, said Thursday as authorities arrested more than 500 people in a nationwide sweep. "We lost an agent, we lost a good agent. And we have to respond."

The massive search for people connected to any Mexican drug cartel working in the United States began Wednesday night as a direct response to the Feb. 15 killing of ICE agent Jaime Zapata in a roadside ambush in Mexico. Fellow ICE agent Victor Avila was wounded in the attack.

As part of the effort coordinated by the Drug Enforcement Administration and ICE, authorities seized at least $10 million in cash and confiscated millions of dollars' worth of illegal drugs. Authorities in Brazil, El Salvador, Panama, Colombia and Mexico conducted similar sweeps in concert with U.S. authorities.

By late Thursday afternoon police and federal agents around the U.S. had seized nearly 300 weapons and more than 16 tons of marijuana along with other drugs. The sweep was expected to continue through Friday.