Agents from U.S. Immigration and Customs Enforcement entered the Agriprocessors Inc. complex in northeast Iowa Monday morning to execute a criminal search warrant for evidence relating to aggravated identity theft, fraudulent use of Social Security numbers and other crimes, said Tim Counts, a Midwest ICE spokesman.

Agents are also executing a civil search warrant for people undocumented in the United States, he said.

Immigration officials told aides to Rep. Bruce Braley, D-Iowa, that they expect 600 to 700 arrests. About 1,000 to 1,050 people work at the plant, according to Iowa Workforce Development, the state's employment services agency.

Chuck Larson, a truck driver for Agriprocessing, was in the plant when the agents arrived. "There has to be 100 of them," he said of the agents.

Larson said the agents told workers to stay in place then separated them by asking those with identification to stand to the right and those with other papers, to stand to the left.

"There was plenty of hollering," Larson said. "You couldn't go anywhere."

When asked who was separated, Larson said those standing in the group with other papers were all Hispanic.

ICE spokesman Harold Ort in Postville did not confirm or deny anyone had been detained, but went on to say the children of those detained would be cared for and "their caregiver situation will be addressed."

"They were asked multiple times if they have any sole-caregiver issues or any childcare issues," Ort said.

Aides to Braley said they have been told "hundreds" of arrests are expected because the action is more of an "investigation" than an immigration raid, and specific individuals are being targeted for arrest as part of the investigation.

Counts described the events in Postville as a "single site operation." He said he was not aware of any other immigration raids being conducted elsewhere Monday.

Postville Police Chief Michael Halse said he did not know anything about the raid until Monday morning.

Postville is a community of more than 2,500 people that includes natives of German and Norwegian heritage and newcomers who include Hasidic Jews from New York, plus immigrants from Mexico, Russian, Ukraine and many other countries.

The Agriprocessors plant, known as the nation's largest kosher slaughterhouse, is northeast Iowa's largest employer.

About 200 Hasidic Jews arrived in Postville in 2087, when butcher Aaron Rubashkin of Brooklyn's Crown Heights neighborhood reopened a defunct meat-packing plant with his two sons, Sholom and Heshy, just outside the city limits. Business boomed at the plant, reviving the depressed economy while pitting the newcomers against the predominantly Lutheran community.

Former Iowa Gov. Tom Vilsack said the Postville immigration investigations were warranted despite concerns federal official violated the constitutional rights of people in past raids.

"Remember our concern has not been about whether or not there should be raids," Vilsack said. "It's the way the raids have been conducted and the way in which American citizens' rights have been violated by virtue of sort of a roundup process that's used and what we think are inappropriate and unconstitutional actions on the part of immigration officials."