An outspoken critic of the Chinese government is under investigation for “economic crimes,” China’s Foreign Ministry announced Thursday. It’s the first time the government has acknowledged the detention of Ai Weiwei, one of the country’s most prominent artists. The government didn’t offer any specifics about the allegations—economic crimes generally include charges like tax avoidance—and his family denounced them, arguing that the way he was arrested proved he was the victim of a political witch hunt. Ai was blocked from leaving China on Sunday and detained, and hasn’t had any contact with his family since. Outgoing American Ambassador Jon Huntsman and other foreign officials have criticized Ai’s detention.