When Youngjin looked out of his office window and saw armored trucks and immigration enforcement officers running around with guns, he was surprised, but not worried.

The young South Korean was certain it had nothing to do with him. He was in the US only for a few weeks on a short-term visa, he thought to himself.

Then the armed agents burst into his room and ordered him outside. They handcuffed him, before attaching chains to his waist and ankles, and loaded him onto a bus bound for a detention center.

I panicked and my mind went blank. I felt sick, he told the BBC, now back home in South Korea.

I couldn't understand why I was being treated like this.

Youngjin is one of more than 300 Korean workers who were detained in the US state of Georgia earlier this month, in one of the largest immigration raids of Donald Trump's presidency to date. He and others interviewed for this article didn't want to reveal their real names to protect their identities.

US officials initially claimed the workers had been in the country illegally on incorrect visas, but eventually, the two sides struck a deal allowing them to leave voluntarily without any penalties, so they could return to work there in the future.

Most of the workers were in the US temporarily, helping to build an electric car battery plant run by two South Korean companies, Hyundai and LG – part of a US push to get foreign companies to invest and manufacture more in the states.

LG said that many of its employees who were arrested held various types of visas or were under a visa waiver program. They were especially shocked by the raid.

We just came out for a brief break, and I could see a lot of people, officials with guns. As Koreans, we just thought they were here to arrest criminals, but then, they suddenly started arresting us, said Chul-yong, another detained worker.

US immigration officials employed helicopters and drones during the raid, a spectacle that left many frightened. There were helicopters and drones, armored vehicles… people with guns, he recalled.

Details of the treatment endured in detention centers emerged from several interviews. Many described being shackled and kept in freezing conditions. I had a panic attack. I just stood there trembling, Youngjin shared about being locked in a room with 60-70 others.

South Korea's Chief Trade Negotiator stated that even the US felt it may have gone a bit too far, following backlash over the methods used during the arrests. The South Korean government is now investigating potential human rights violations related to the raid.

After newly revealed reports, the incident has strained U.S.-South Korea relations, coming just after a trade deal aimed at strengthening economic ties.