SEOUL, South Korea (AP) -- South Korea's foreign minister will travel to the U.S. on Monday to finalize steps for the return of several hundred South Korean workers detained last week in a massive immigration raid in Georgia, as the incident caused confusion, shock and a sense of betrayal among many in the U.S.-allied nation.

The Sept. 4 raid at a battery factory of the Hyundai plant in Georgia led to the detainment of 475 workers, more than 300 them South Koreans, some of whom were shown being shackled around their hands, ankles and waists in video released by U.S. Immigration and Customs Enforcement.

South Korea announced Sunday the U.S. agreed to release the detained workers, saying it would send a charter plane to bring them home once final administrative steps are completed.

U.S. President Donal Trump, who earlier backed the raid, said Sunday night that the U.S. could work out an arrangement with South Korean workers to train U.S. citizens to do work such as battery and computer manufacturing.

Appearing at a parliamentary hearing before his departure, Foreign Minister Cho Hyun called the raid "a very serious matter" that he hadn't anticipated at all, as many lawmakers lamented the American operation.

"If U.S. authorities detain hundreds of Koreans in this manner, almost like a military operation, how can South Korean companies investing in the U.S. continue to invest properly in the future?" said Cho Jeongsik, a lawmaker from the liberal governing Democratic Party.

Another lawmaker, Kim Gi-hyeon from the conservative opposition People Power Party, said the "unacceptable" raid dealt South Korea a "severe blow that will be difficult to heal."

Some lawmakers even called for the government to retaliate by investigating Americans who are alleged to work illegally in South Korea.

Seoul has expressed regret over the raid, but experts say it won't likely take any major tit-for-tat measures given the country's security dependence on the U.S. in deterring potential North Korean aggressions and other spheres of cooperation between the two countries, including business ties.

The Georgia operation was the latest in a series of workplace raids performed as part of the Trump administration's mass deportation agenda, but it was Homeland Security Investigation's largest enforcement operation on a single site. Many observers note that the state of Georgia is a symbol of the economic cooperation between the two countries since many large South Korean businesses operate factories and plan future investments there.

In South Korea, many remain stunned at the raid that came after the country in late July promised to pour hundreds of billions of dollars into U.S. investments as part of a tariff deal. In late August, Trump and South Korean President Lee Jae Myung also held their first summit meeting in Washington.

"The way that Trump is pressuring the Korean government and inflicting damages on its people is very rough and unilateral," said Kim Taewoo, former head of Seoul's Korea Institute for National Unification. "Can this be forgotten easily in South Korea? In a long-term perspective, it won't be good for U.S. national interests as well."

In an editorial Monday, South Korea's biggest newspaper, Chosun Ilbo, wrote that "Fundamental doubts emerge: What does the U.S. mean by 'alliance,' and are investment benefits guaranteed across administrations?"

Paik Wooyeal, a professor at Seoul's Yonsei University, viewed the raid as a collision between a U.S. goal of reshoring manufacturing with foreign investments, and a lack of visa and immigration systems that could support such an attempt.

Paik said that South Korean companies operating in the U.S. will likely suffer "a great confusion" as they would be forced to bring their workers back home to resolve visa issues. Such developments would also undermine U.S. interests, but Trump won't likely make any concessions anytime soon, Paik said.

Steven Schrank, the lead Georgia agent of Homeland Security Investigations, said Friday that some of the detained workers had illegally crossed the U.S. border, while others had entered the country legally but had expired visas or had entered on a visa waiver that prohibited them from working.

But South Korean officials and experts have expressed frustration over what they call the United States' strict limits on H-1B or H-2B visas for high-skilled foreign workers to protect its domestic workforce, and its inaction on Seoul's calls to expand work visas for skilled South Korean nationals. As a result, South Korean companies have been relying on short-term visitor visas or the Electronic System for Travel Authorization to send workers needed to launch manufacturing facilities or handle other setup tasks.

"The incident will inevitably exacerbate shortages of skilled workers with legal work authorization and create pressure for increases in labor costs, potentially disrupting operations and rising costs across major business projects in the United States," South Korea's Eugene Investment and Securities said in a report Monday.

Daishin Securities in a report said the Georgia raid could delay operations at the targeted battery plant, which was slated to begin production early next year, potentially affecting Hyundai's EV business in America.

During Monday's parliamentary hearing, Cho, the foreign minster, told lawmakers that the U.S. had "not responded adequately" to South Korea's requests to expand skilled visas for its workers, and that Seoul plans to use the Georgia raid as an opportunity to move related negotiations forward.

Cho said that some of the people detained in Georgia may need to return to the site to complete work at the factory, and that South Korean officials are negotiating with American authorities to ensure that those detained can reenter the United States.

"I will clearly point out to them that a delay in (the factory's) completion would also cause significant losses for the United States," Cho said.