South Koreans suspected of working in the United States illegally were the majority of 475 people arrested in a raid on a Hyundai-LG battery plant being built in the southern state of Georgia, a U.S. official said Friday.

Steven Schrank, a Homeland Security Investigations special agent in Atlanta, said the operation was the largest single site raid carried out so far as part of President Donald Trump's nationwide anti-migrant drive.

Thursday's raid stemmed from a "criminal investigation into allegations of unlawful employment practices and serious federal crimes" at the Hyundai Motor-LG Energy Solution joint venture plant in the town of Ellabell, Schrank told reporters.