DES MOINES, Iowa (AP) — A federal immigration raid at a kosher meatpacking plant in northeast Iowa was the largest such operation in U.S. history, with nearly 400 people arrested, federal officials said Tuesday.

Immigration and Customs Enforcement officials said at least 390 people were arrested on immigration charges as part of a raid Monday morning at Agriprocessors Inc. in Postville. The plant had about 900 workers before the raid.

Most of the 314 men and 76 women arrested are from Guatemala and Mexico, but some were from Ukraine and Israel.

The raid followed a months-long investigation into Agriprocessors, the largest kosher slaughterhouse in the world.