DETROIT (Reuters) - A battery plant co-owned by Hyundai Motor is facing a minimum startup delay of two to three months following an immigration raid last week, Hyundai CEO Jose Munoz said on Thursday. 

The Georgia plant, which is operated through a joint venture between Hyundai and South Korea's LG Energy Solution, was at the center of the largest single-site enforcement operation in the U.S. Department of Homeland Security's history last week. 

Munoz, in his first public comments since the raid, said he was surprised when he heard the news and immediately inquired if Hyundai workers were involved. He said the company discovered that the workers at the center of the raid were mainly employed by suppliers of LG. 

"For the construction phase of the plants, you need to get specialized people. There are a lot of skills and equipment that you cannot find in the United States," Munoz said on the sidelines of an automotive conference in Detroit.

The plant, part of a $7.6 billion factory complex to make battery-powered models, was slated to come online later this year. 

About 475 workers, including more than 300 South Koreans, were arrested, according to U.S. immigration officials. The raid was conducted over suspicions about the "unlawful" visa and immigration status of workers at the site, U.S. officials have said.

A plane carrying the workers is flying them home from Atlanta, after Seoul and Washington agreed to their release and to discuss setting up a visa programme for workers needed at such sites being constructed by South Korean businesses.

Hyundai Motor Group Executive Chair Euisun Chung said on Thursday he was "really worried about that incident" but was relieved the workers were returning home to South Korea.

"Maybe our government and the U.S. government, they are working closely, and the visa regulation is very complicated," Chung said at the Detroit conference. "And I hope we can make it together a better system."

It is typical for an automotive battery plant to employ these workers as it is getting off the ground, Munoz said. 

Munoz said Hyundai will source batteries from other plants as it waits for the LG plant to start up, including from a Georgia plant co-owned with Korean battery-maker SK On.

Fallout from the raid has cascaded across the country. Reuters first reported that workers at other LG plants, including those co-owned by GM, were asked to return home.