A court in Cambodia has imposed a heavy fine on a leading opposition politician after finding him guilty of defamation for saying that nationwide local elections in June were unfair.

Son Chhay, deputy president of the Candlelight Party, had said in an online interview after the polls that the National Election Committee was biased in favour of the governing Cambodian People’s Party. He also alleged there was vote-buying and intimidation of voters.

The National Election Committee and the Cambodian People’s Party each sued the veteran politician for defamation.

The Phnom Penh Municipal Court fined Son Chhay nine million riel (£2,023) in the election committee case. In the case filed by the Cambodian People’s Party, he was ordered to pay a fine of eight million riel (£1,798) to the state and 30 billion riel (£674,516) in compensation to the governing party.

The Candlelight Party is likely to be the biggest and most credible party challenging Prime Minister Hun Sen’s Cambodian People’s Party in next year’s general election.

The governing party faced a much stronger challenge ahead of the 2018 election from the highly popular Cambodia National Rescue Party. But it was disbanded just months ahead of the polls by a controversial court ruling that it had plotted the illegal overthrow of the government.

Cambodian courts are widely believed to be under the influence of the government, and the disbanding of the governing party’s main rival allowed it to sweep up all the seats in the National Assembly.

Virtually all of the former Cambodia National Rescue Party leaders are in hiding, in jail or in self-imposed exile abroad, fearing arrest.

The Candlelight Party is the unofficial successor to the Cambodia National Rescue Party. The governing party won June’s local elections with 74.3% of the votes, with the Candlelight Party receiving about 22.3%.

The large fine imposed on Son Chhay, the most prominent figure in the Candlelight Party, will pressure the opposition party ahead of next year’s polls, especially since it operates on a shoestring budget. Hun Sen’s party controls the levers of government and is close to nearly all newspapers and broadcasters.

The Cambodian People’s Party has held an iron grip on power for decades and controls almost every level of government. Hun Sen, an authoritarian ruler in a nominally democratic state, has held power for 37 years.

In recent years, his government has aggressively pursued legal action against its opponents, hindering their ability to operate freely, and sometimes hounding them into exile or jailing them.

Speaking to reporters on Friday after the verdict was issued, defence lawyer Choung Chou Ngy called the decision an injustice and said he will talk to Son Chhay about lodging an appeal.

“This story is a political case and from my observation, I have seen that they wanted to kick him out from entering the political arena,” the lawyer said.