South Korea’s foreign ministry announced Friday that it is sending personnel to a US Hyundai-LG battery plant where more than 300 Korean citizens were detained in an immigration raid the previous day, according to local media. Foreign Ministry spokesperson Lee Jae-woong said South Korea voiced concerns to the US embassy in Seoul and called on US authorities to respect the country’s economic activity and citizens following the raid in Bryan County, Georgia.

US officials said over 475 persons, mostly Korean nationals, were detained during the execution of a search warrant by Immigration and Customs Enforcement (ICE), Homeland Security Investigations (HSI), the FBI, and other agencies. According to local media, Homeland Security agents were investigating “unlawful employment practices” at the site.

HSI Special Agent in Charge Steven Schrank said at a press conference that the raid was “the largest single-site enforcement operation in the history of [HSI]” and that agents found undocumented immigrants and foreign nationals who were not authorized to work being employed by various companies. Schrank elaborated:

This was not an immigration operation where agents went into the premesis, rounded up folks, and put them on buses. This has been a multi-month criminal investigation where we have developed evidence, conducted interviews, gathered documents, and presented that evidence to the court in order to obtain a judicial search warrant.

Schrank added that the investigation “is an ongoing matter” and that no criminal charges are being announced yet.

The Trump administration has received international scrutiny over its immigration enforcement practices. On Tuesday, a federal judge ruled that President Donald Trump’s deployment of National Guard troops to Los Angeles over mass anti-ICE demonstrations was illegal. ICE has also been accused of illegally detaining US citizens and racial profiling.