(Bloomberg) -- Taipei prosecutors are investigating the former vice minister of defense over concerns over his contact with a Chinese spy ring in what is being described as Taiwan’s biggest ever espionage case.

Former Vice Defense Minister Chang Che-ping is being probed for accepting hospitality, including multiple meals and trip by his wife to Hong Kong, from people connected to a Chinese intelligence organization while he was previously serving as the commander of Taiwan’s Air Force Combatant Command, Taipei-based Mirror Media reported Wednesday, citing unidentified sources.

Taipei District Prosecutors Office confirmed they were investigating Chang without explaining what he is suspected of.

Chang said he regretted the harm the report caused the military and his family. While he didn’t deny contact with the alleged Chinese spy, he insisted he had never leaked any sensitive information and that the family had paid for all of his wife’s trips to China. “I never did or said anything illegal,” he said.

The investigation is the latest incident to highlight Chinese intelligence-gathering efforts as ties between China on the one side and Taiwan and its prime military backer, the U.S., become increasingly fraught. The issue could raise U.S. concerns about Taiwan’s ability to keep technology and other secrets out of Beijing’s hands.

China claims Taiwan as part of it territory, and frequently reiterates its intension to bring it under Communist control, by military means if necessary. The U.S. opposes Beijing’s efforts to impose its will on the democratically run island and has promised to supply weapons so Taiwan can defend itself.

Chinese Foreign Minister Wang Yi reiterated Beijing’s demands for the U.S. to stay out of issues it deems to be its core interests, including Taiwan, during contentious talks with U.S. Deputy Secretary of State Wendy Sherman on Monday in Tianjin.

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Taiwanese investigators have been probing this latest Chinese intelligence network for the past five years, according to the Mirror Media report. They say the Guangzhou branch of the Central Military Commission’s Political Work Department first sent a Hong Kong-based businessperson to Taiwan in 2012, successfully recruiting several retired military officials, including two generals, to provide information about the island’s military.

The Hong Kong recruiter met with Chang several times in 2015 and 2016 and even paid for a trip by Chang’s wife to the former British colony, according to the report.

While Chang was the commander of the Air Force Combatant Command at the time of the alleged contacts, he subsequently rose through the ranks to become vice defense minister in 2019, Taiwan’s No. 3-ranking military officer after the minister and the chief of the general staff. The level of his contact with Chinese agents concerns Taiwan’s national security officials so much that he was removed from his position on July 1 and made the head of Taiwan’s National Defense University.

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