U.S. immigration authorities on Wednesday rounded up hundreds of undocumented workers in food processing plants during a sprawling operation in Mississippi that officials touted as the largest immigration enforcement sweep in a single state in U.S. history.

By targeting workplaces across six different cities in southern Mississippi, Immigration and Customs and Enforcement (ICE) agents, with the help of the local district attorney's office, apprehended approximately 680 undocumented immigrants.

At a press conference on Wednesday afternoon, U.S. Attorney for the Southern District of Mississippi Mike Hurst said the large-scale raids collectively represented "the largest single state immigration enforcement operation in our nation's history."

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"While we are a nation of immigrants, more than that, we are first and foremost a nation of laws," he told reporters at the press conference, where he was flanked by Acting ICE Director Matthew Albence.

Handcuffed female workers are escorted into a bus for transportation to a processing center following a raid by U.S. immigration officials at a Koch Foods Inc., plant in Morton, Miss., Wednesday, Aug. 7, 2019. AP

Hurst said authorities relied on both criminal and administrative warrants to execute Wednesday's raids at seven different work sites. Administrative warrants are usually used by ICE to detain people who are in the U.S. unlawfully but otherwise do not have criminal records.

Albence, who was tapped last month to serve as acting director for a second time, said his agency would look to "swiftly" deport the apprehended workers with open orders of removal. Some, he added, would be prosecuted criminally.

Those without criminal records or orders of deportations will be placed in immigration proceedings before a judge and may be released.

An ICE official on Thursday told CBS News "several hundred" of the workers apprehended were released, while the agency determined that others will be moved to a detention facility.

Koch Foods Inc., employees leave the Morton, Miss., plant following a raid by U.S. immigration officials in Morton, Miss., Wednesday, Aug. 7, 2019. AP

While officials on Wednesday framed the operation as a crackdown on employers who hire undocumented workers, advocates have long denounced an apparent disparity between the prosecution of unauthorized immigrants and the people and companies who employ them.

Researchers at Syracuse University in New York found that between April 2018 and March of this year, just 11 individuals were criminally prosecuted for knowingly hiring unauthorized workers and only three of them were sentenced to time in prison. No companies were prosecuted. During that same time span, more than 85,000 immigrants were prosecuted for illegal entry.

On Wednesday afternoon, Magdalena Gomez Gregorio tearfully pleaded for the return of her dad, one of hundreds of undocumented immigrants rounded up Wednesday by ICE.

"My dad didn't do nothing. He's not a criminal," she said through tears.

The 11-year-old and other children of those arrested stayed at a community center gymnasium overnight after about 600 immigration agents targeted food processing plants across central Mississippi. Some employers were also arrested.

Asked about what would happen to workers who have children in the U.S., Albence reiterated the administration's standard guidance that arrests in the criminal justice system lead to family separations. He said affected children would be placed with other family members and in some instances, some parents could be released with ankle bracelets.

In Forest, Mississippi, gym owner Jordan Barnes and other community leaders were taking donations to put some of the children up for the night in his Clear Creek Boot Camp and get them to school Thursday morning, reports CBS Jackson, Mississippi affiliate WJTV.

The station says many children of those arrested across the state were left with nowhere to go. Children, some as young as toddlers, were relying on neighbors and even strangers to pick them up and drive them to the gym, where people tried to keep them calm. But many of them couldn't stop crying for their parents, WJTV said.

Peco Foods, a poultry processing and packaging company, confirmed that ICE conducted operations at three of its facilities in southern Mississippi.

The raids drew quick and scathing condemnation from immigrant advocates and Democrats.

Julia Solórzano, a legal fellow at the Southern Poverty Law Center, said these types of large-scale workplace operations "terrorize" and "destroy" communities, while accomplishing little for the administration.

"For a lot of the cities where these raids occurred, it was the first day of school. We know from past immigration enforcement actions of this type, that there are going to be children who go home tonight and their parents will be gone," Solórzano told CBS News. "It's extremely disruptive to families. It's — in many cases — depriving the family of the primary breadwinner."

Denouncing the operation, Rep. Joaquin Castro of Texas, who is chairman of the Congressional Hispanic Caucus, accused the administration of sowing fear in Latino and immigrant communities.

"Let's be clear: ICE raids of this scale are not conducted for the purpose of immigration enforcement, they're to strike fear in our communities in a time when Latinos are already living in terror," the Texas Democrat wrote in a statement.

Claudia Valenzuela, an attorney at the American Immigration Council, said the workers apprehended will have a difficult time finding counsel rapidly because predominantly rural Mississippi does not have as robust of a presence of legal aid and pro-immigrant groups, compared to states with large immigrant and Latino communities like New York and California.

She said the magnitude of the operation alone would present challenges to any community, even those with well-established networks of advocacy organizations ready to represent and help undocumented immigrants.

"It would be hard for a city like Chicago or New York to respond in the wake of such a large-scale raid," Valenzuela said.