China and Taiwan have been ruled separately since 1949, but Beijing insists the island is part of its territory and has vowed to seize it one day.

There has been a series of spying cases in Taiwan, as China maintains military and political pressure on Taipei to accept its claims of sovereignty.

In the latest case, the accused included three members of a military unit in charge of security for the Presidential Office, presidential spokesman Wen Lii said.

A fourth person was a soldier in the defence ministry's information and telecommunications command.

They allegedly used their mobile phones to photograph military information, which was passed to "Chinese agents", the Taipei district prosecutors office said.

Lii condemned "any treasonous behaviour that harms the people and the country".

"China has long used various means to infiltrate, coerce and suppress our country, and intends to divide and destroy the hard-won democracy and freedoms of the Taiwanese people," Lii said in a statement.

"Both soldiers and civilians must unite to protect our homeland. If an officer or soldier commits treason or betrayal of the people for personal selfish interests, it will be extremely disgraceful and should be severely condemned and punished by law."

The four received payments ranging from around NT$260,000 to NT$660,000 ($8,000-$20,000) "depending on the confidentiality level of the military information they provided", prosecutors said, without elaborating on the content of the material.

The incidents happened from 2022 to 2024.

Three of the soldiers were discharged before an investigation was launched in August this year following a tip-off to the defence ministry.

The fourth was suspended in August.

All four have been detained and charged with corruption and violating national security law for "leaking and delivering confidential information or electromagnetic records for China".

They face a maximum seven years in jail if convicted.

"The Chinese Communist Party's infiltration campaign against us has never stopped," the defence ministry said in a statement, describing the four accused as "treasonous and lawless".

"In order to actively prevent enemy espionage activities, the military will also continue its counter-intelligence education," it added.

In September, an ex-air force instructor was sentenced to 17 years in prison for "aiding the enemy" and delivering military secrets to China.