SEOUL, South Korea (AFP) — Seoul said Sunday that negotiations with the United States to secure the release of South Korean workers detained in an immigration raid have been "concluded" and they would soon be freed and flown home.

It follows the arrest of more than 300 South Korean workers at a Hyundai-LG battery plant being built in the southern state of Georgia on Thursday.

The operation, carried out in the town of Ellabell, was the largest single site raid implemented so far under President Donald Trump's nationwide anti-migrant drive, catching Seoul officials off guard.

"As a result of the swift and united response... negotiations for the release of the detained workers have been concluded," Kang Hoon-sik, chief of staff to President Lee Jae Myung, said on Sunday.

"Only administrative procedures remain. Once these are completed, a chartered flight will depart to bring our citizens home," he added.