Chang Che-ping, in office from July 2019 to June 2021, was being probed for allegedly having multiple contacts with a Chinese spy organisation over meals, online news website Mirror Media reported citing sources, in what could be the island's highest level espionage case yet.

Taiwan and China have been spying on each other since the Nationalists fled to the island to set up a rival government in 1949, having lost the civil war on the mainland to the communists.

Beijing has ramped up pressure since the 2016 election of President Tsai Ing-wen, as she rejects its stance that the self-ruled, democratic island is part of China's territory.

When asked to comment on the report on Wednesday, Taipei district prosecutor's office confirmed an investigation was underway but had not concluded.

The office declined to elaborate further.

Mirror Media said Chang was being probed for meeting privately with a Hong Konger in charge of a spying group and received gifts from that person while he was chief of the Air Force Combatant Command.

His wife also accepted a paid-for trip to Hong Kong, the report said.

Chang, 63, was once a frontrunner to become chief of the general staff but he was eventually assigned to head the National Defence University.

The Mirror Media report said the unnamed Hong Konger who allegedly attempted to recruit Chang had been developing a spy network under the disguise of doing business since Tsai's predecessor Ma Ying-jeou, who was president between 2008 and 2016.

He was linked to China's Central Military Commission and had successfully recruited several retired Taiwanese officers, the outlet added, citing unnamed sources.

Chang has denied any wrongdoing and claimed he strictly followed all confidentiality requirements during meetings with friends, Taiwan's official Central News Agency said.