U.S. Immigration and Customs Enforcement officers carry out a raid as part of Operation Cross Check in Sherman, Texas, on June 20, 2019.

Immigration enforcement authorities raided food processing plants across Mississippi on Wednesday, picking up 680 workers in what was being billed as the biggest single-day, one-state sweep in U.S. history, officials said.

The raids hit seven plants in six cities, and most of the workers arrested are Latino.

"While we are a nation of immigrants, more than that, first and foremost, we are a nation of laws," said U.S. Attorney Mike Hurst of the Southern District of Mississippi. "They have to come here legally or they shouldn't come here at all."

Hurst also chastised businesses for using undocumented immigrants.

"To those who use illegal aliens for competitive advantage or to make a quick buck, we have something to say to you: If we find that you have violated federal criminal law, we're coming after you," he said.

The long-planned raids unfolded as President Donald Trump traveled to El Paso, Texas, where 22 people were killed Saturday — allegedly by a man linked to an online screed about the "invasion" of Hispanic immigrants.

Trump has long railed against illegal immigration and began his presidential campaign by declaring that Mexican immigrants are "bringing drugs, they're bringing crime" and that they're "rapists."

The acting director of Immigration and Customs Enforcement, Matthew Albence, said there was no connection between the timing of these raids and Trump's El Paso trip.

"This is a long-term operation that's been going on," Albence said. "Our enforcement operations are being done on a racially neutral basis. Investigations are based on evidence."

Albence told The Associated Press that the raids could be the largest such operation thus far in any single state.

In light of Wednesday's raids, the American Civil Liberties Union and the Southern Poverty Law Center both issued advisories urging anyone approached by ICE to remain silent, not open any doors without seeing a warrant, and demand to speak to a lawyer.

"It was a sad situation inside," said Domingo Candelaria, a legal resident and worker at Koch Foods Inc. in Morton, Mississippi, about 40 miles east of Jackson, where one of the raids took place.

The detained workers were expected to be processed at a hangar at the Mississippi National Guard in Flowood, near Jackson.