Taipei prosecutors indicted four people on Tuesday suspected of spying for China in a case that reached Taiwan's presidential office, seeking jail terms of more than 18 years.
Democratically-governed Taiwan says it has faced heightened military and political pressure over the past five years or so from Beijing, which views the island as sovereign Chinese territory, a position Taipei's government rejects.
In a statement, Taipei prosecutors said the four, all previously members of the ruling Democratic Progressive Party, had been indicted on espionage and other charges.
One of them was a former assistant to then foreign minister Joseph Wu, now head of the National Security Council, while another was a former presidential office adviser, sources familiar with the matter have previously told Reuters.
The Taipei prosecutors said in a statement that their suspected crimes included divulging or delivering classified national security information to China.
Jail sentences of 18 years or more are being sought, the statement added.
Reuters was not able to immediately locate contact details for legal representatives of any of those indicted.
China's Taiwan Affairs Office did not respond to a request for comment.
Last week, Taiwan's presidential office said it could not comment on the cases given the ongoing legal proceedings.
But it said that any person, regardless of party affiliation, who has "betrayed the country, collaborated with hostile external forces and committed crimes that hurt the whole nation" should be subject to the most severe punishment.
