Reuters was unable to reach Son for comment.
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Son plays for the South Korean national team and Chinese Super League club Shandong Taishan, based in the northeastern province of Shandong.
“China is a country governed by the rule of law and handles the relevant cases in accordance with the law to protect all the legitimate rights and interests of the parties involved,” ministry spokesperson Wang Wenbin told a news briefing.
South Korea’s foreign ministry said its mission in China was providing necessary consular support to Son, but declined to comment further, citing privacy.
A Korea Football Association official said it had reached out to Shandong Taishan, seeking an explanation, but has not heard back.
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Son played in three of the national team’s four games during the World Cup last year in Qatar, where South Korea reached the elimination round of the tournament for the first time in 12 years.
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His club has not commented publicly on Son’s situation, but uploaded a poster wishing him happy birthday on Friday, the day of his detention.