The number of people prosecuted for spying for Beijing has risen sharply in recent years, with retired and serving members of Taiwan's military the main targets of Chinese infiltration efforts, official figures show.

It comes after President Lai Ching-te announced this month plans to reinstate military judges to hear Chinese espionage cases and other offences involving Taiwanese service members.

Three members of a military unit in charge of security for the Presidential Office, and a soldier in the defence ministry's information and telecommunications command were convicted for violating national security law, the Taipei district court said on Wednesday.

"Their acts betrayed the country and endangered national security," the court said in a statement.

The four received jail terms ranging from five years and 10 months to seven years for passing "internal military information that should be kept confidential to Chinese intelligence agents for several months", the court said.

The crimes took place between 2022 and 2024, the court said, adding that the four had received payments ranging from around NT$260,000 to NT$660,000 ($7,850-$20,000), it said, without specifying what kind of information was leaked.

The defendants had worked for "extremely sensitive and important units but violated their duties to accept bribes, and stole secrets by photographing," the statement said.

Prosecutors said the soldiers had used their mobile phones to photograph military information.

Three of the soldiers were discharged from the military before an investigation was launched in August last year following a tip-off to the defence ministry, and the fourth was suspended.

Taiwan's intelligence agency previously reported that 64 people were prosecuted for Chinese espionage in 2024, compared with 48 in 2023, and 10 in 2022.

Beijing claims the self-ruled island as part of its territory and has threatened to use force to bring it under its control.

Both sides of the Taiwan Strait have been spying on each other for decades.

But analysts have warned that espionage is a bigger problem for Taiwan, which faces the existential threat of a Chinese invasion.