South Korea’s government says it has reached an agreement with the US to release its citizens detained in a massive immigration raid at a Hyundai plant in Georgia.

The chief of staff of South Korea’s president said a chartered plane would be sent to bring the detainees home if administration procedures were completed.

Kang Hoon-sik said the authorities were trying to improve the visa system to prevent such incidents in the future.

US officials detained 475 people – more than 300 of them South Korean nationals – who they said were found to be illegally working at the battery facility, one of the largest foreign investment projects in the state.

Media in both countries report that South Korean Foreign Minister Cho Hyun is expected to travel to the United States on Monday.

The White House has defended the operation at Hyundai, dismissing concerns that the raid could deter foreign investment. President Donald Trump took aim at the raid in a post on social media and called for foreign companies to hire Americans.

“I am hereby calling on all Foreign Companies investing in the United States to please respect our Nation’s Immigration Laws,” Trump said in the post on Sunday.

He said the US would make it easy for foreign companies to legally bring their “great technical talent, to build World Class products” but, asked that in return, these companies “hire and train American Workers”.

A worker at the plant spoke to the BBC about the panic and confusion during the raid. The employee said the vast majority of the workers detained were mechanics installing production lines at the site, and were employed by a contractor.

He also said a minority of those arrested had been sent from head office in Seoul and had been carrying out training, which the BBC has not been able to confirm.

More extensive immigration raids like the operation at the plant are likely, Trump administration border tsar Tom Homan told CNN’s State of the Union on Sunday.

“We’re going to do more work site enforcement operations,” Homan said.

“No one hires an illegal alien out of the goodness of their heart. They hire them because they can work them harder, pay them less, undercut the competition that hires US citizen employees.”

Video released by ICE officials showed Asian workers shackled in front of a building, with some wearing yellow vests with names such as “Hyundai” and “LG CNS”.

“People on short-term or recreational visas are not authorized to work in the US,” ICE said, adding that the raid was necessary to protect American jobs.

“This operation sends a clear message that those who exploit the system and undermine our workforce will be held accountable,” Homeland Security Investigations (HSI) Special Agent Steven Schrank said in a statement on Saturday.

South Korea, a close US ally, has pledged tens of billions of dollars in American manufacturing investment, partly to offset tariffs.

The timing of the raid, as the two governments engage in sensitive trade talks, has raised concern in Seoul.

Trump has actively encouraged major investments from other countries while also tightening visa allocations for foreign companies.

LG Energy Solution, which operates the plant with Hyundai, says many of the LG employees arrested were on business trips with various visas or under a visa waiver programme.

The company has said it is suspending most business trips to the US and directing employees on assignment in the US to return home immediately.

South Korean media widely described the raid as a “shock,” with the Dong-A Ilbo newspaper warning it could have “a chilling effect on the activities of our businesses in the United States”.

The factory, which makes new electric vehicles, had been touted by Georgia’s Republican governor as the biggest economic development project in the state’s history, employing 1,200 people.

The arrested workers are being held at an ICE facility in Folkston, Georgia.

LG Energy Solution said 47 of its employees and about 250 workers for contractors at the joint venture factory were detained.