TAIPEI • A court in Taiwan has sentenced former president Ma Ying-jeou to four months' jail over a leak of information related to national security, legal documents showed, but he has vowed to appeal, and could avoid jail altogether by paying a fine.

In the first conviction in a series of legal actions against Ma since he left office in 2016, Taiwan's High Court overturned a lower court's judgment of not guilty.

"Ma Ying-jeou violated the Communication and Surveillance Act," it said in its judgment yesterday, adding that the punishment was four months' imprisonment.

His sentence could, however, be avoided on payment of a NT$120,000 (S$5,400) fine, the court said in a statement, in line with Taiwan law that allows such payments for lighter sentences, instead of going to jail.

Ma told Taiwan media he planned to appeal. "This case is a type of constitutional lawsuit," he said. "What I'm fighting for is not just my own rights, but it's also related to how the authority of Taiwan's future presidents should not be limited."

He added: "Therefore, I definitely need to clarify this problem. I definitely will appeal."

Ma, who governed from 2008 to 2016 and championed closer ties with China, became Taiwan's third consecutive president to face criminal charges after leaving office.

Beijing has taken an increasingly hostile stance over the past two years towards Taiwan, following the election of Ms Tsai Ing-wen of the pro-independence Democratic Progressive Party (DPP).

Ma's predecessor, DPP's Chen Shui-bian, was granted medical parole in 2015 while serving a 20-year prison sentence following his corruption conviction.

Mr Lee Teng-hui, who oversaw Taiwan's transition to direct democracy as president from 1988 to 2000, was found not guilty of money laundering and embezzling government funds in November 2013.

The High Court judge found that Ma had improperly disclosed a wiretapped June 2013 conversation between former legislative speaker Wang Jin-pyng and a DPP lawmaker who had recently been acquitted of breach-of-trust allegations.

Ma accused Mr Wang of pressuring prosecutors not to appeal against the acquittal of the lawmaker Ker Chien-ming. While Mr Wang was never indicted for wrongdoing, Mr Ker sought charges against Ma for the leak.

The former president was found to have broken the law by discussing details of the call with the then premier and his deputy secretary-general, according to the court.

REUTERS, BLOOMBERG