Almost 500 people have been arrested at a Hyundai factory in the US state of Georgia by immigration authorities in the largest workplace raid of President Donald Trump’s second term.

A majority of those detained at the 3,000-acre site, which was built by the Korean company to manufacture electric vehicles and has been operational for a year, are Korean nationals.

South Korea expressed “concern and regret” over the operation and urged the US government to respect the rights of its citizens.

The Department of Homeland Security told the BBC that agents executed a search warrant due to allegations of “unlawful employment practices and other serious federal crimes”.

“This was not an immigration operation where agents went into the premises, rounded up folks and put them on buses,” Steve Schrank, the special agent in charge of Homeland Security Investigations in Atlanta, said at a news conference on Friday.

“This has been a multi-month criminal investigation where we have developed evidence, conducted interviews gathered documents and presented that evidence… in order to obtain a judicial search warrant,” Schrank added.

He said it was “the largest single-site enforcement operation in the history of homeland security investigations”.

The raid raises a possible tension between two of President Donald Trump’s top priorities – building up manufacturing within the US and cracking down on illegal immigration. It could also put stress on the country’s relationship with a key ally.

President Trump said in the Oval Office on Friday: “They were illegal aliens and ICE was just doing its job.”

Asked by a reporter about the reaction from Seoul, he said: “Well, we want to get along with other countries, and we want to have a great, stable workforce.

“And we have, as I understand it, a lot of illegal aliens, some not the best of people, but we had a lot of illegal aliens working there.”

“These [workers] are people that came through with Biden. They came through illegally.”

Some 475 people who were in the country illegally or working unlawfully were detained in the operation, immigration officials said.

They were being held at a US Immigration and Customs Enforcement (ICE) facility in Folkston, Georgia, until the agency decides where to move them next.

Of those detained, 300 are reported to be Korean nationals.

In a statement, Hyundai Motor Company said it was “closely monitoring the situation and working to understand the specific circumstances”.

“As of today, it is our understanding that none of those detained are directly employed by Hyundai,” it said.

Hyundai’s production of electric vehicles at the sprawling site was not affected, Reuters reported. Its partner in the battery joint venture, South Korea’s LG Energy Solutions, had paused construction work at the site.

Videos on social media show agents lining workers up and telling them they have a warrant to search the facility. The agents can also be seen talking to some of the employees in the videos.

South Korea said it was dispatching diplomats to the site in response to the raid and that it had contacted the US embassy in Seoul to urge the US “to exercise extreme caution” when it came to Korean citizens’ rights.

“The economic activities of Korean investment companies and the rights and interests of Korean citizens must not be unfairly infringed upon during US law enforcement operations,” South Korea’s foreign ministry said in a statement.

Trump has worked to bring in major investments from other countries while also levying tariffs he says will give manufacturers incentives to make goods in the US.

South Korean companies have promised to invest billions of dollars in key US industries in the coming years, partly as a way to avoid tariffs.

Georgia’s Governor, Republican Brian Kemp, had touted Hyundai’s new electric vehicle operation as the biggest economic development project in the state’s history, employing 1,200 people.

But the president also campaigned on cracking down on illegal immigration, telling supporters he believed migrants were stealing jobs from Americans.

Upon returning to office, he launched a massive effort across the country to round up people thought to be in the US illegally, hold them in detention facilities, and frequently deport them.

While many of those caught in the sweeps have ties to Latin American countries, people of other nationalities have also been arrested.