Taiwan arrested three former military officials over suspicions that they leaked military secrets to China, highlighting the long-enduring hostility between the two as Beijing still considers the island as part of its territory.

Chang Chih-hsin, a former head of the political warfare division at the navy’s meteorology and oceanography office, was arrested following investigations that began in March this year, Taiwan’s defence ministry said in a statement.

“Chang, who initiated contacts with Chinese mainland officials while still serving in the navy, was suspected of luring his former colleagues and making illegal gains,” the statement said.

Defence ministry spokesman David Lo confirmed two other former military officers had been arrested but declined to disclose their titles, reports the Financial Times.

The ministry downplayed the possible damage to Taiwan’s security, claiming no classified information had been compromised and no actively serving officers were involved in the case. “Chang had had limited access to sensitive information of the naval METOC,” Mr. Lo said.

However, the naval METOC kept highly classified information such as mapping and charting publications of the meteorological and oceanographic battle environment used by the island’s submarines and other warships, Taipei-based broadsheet Apple Daily quoted a retired naval general as saying.

“If China had the classified info, it could be able to be aware of the operation of Taiwan’s submarines,” the retired naval general warned.

Taiwan has long fought for independence while China reiterates reunification will happen, by force if necessary. Relations have improved since Beijing-friendly President Ma Ying-jeou came to power in 2008 and sought to diffuse tensions by strengthening trade and tourism ties.