US immigration authorities have detained some 680 undocumented immigrants in what a federal prosecutor described as a record-setting operation.

US Attorney for the Southern District of Mississippi Mike Hurst told reporters the arrests took place at seven sites in six different cities in Mississippi on Wednesday. The raids, he said, are “believed to be the largest single-state immigration enforcement operation in our nation’s history.”

Officials declined to provide details about what sites had been targeted, citing what they said was an ongoing criminal investigation.

The arrests came as a result of administrative and criminal search warrants executed by special agents from Homeland Security Investigations, Hurst said.

“Today, through the hard work of these men and women, we are once again becoming a nation of laws,” he said.

Immigration and Customs Enforcement has stepped up worksite enforcement  since President Donald Trump took office, conducting a number of large-scale raids at food-processing plants and gardening centers in recent years.