PHNOM PENH (Reuters) - Cambodian Prime Minister Hun Sen filed a $1-million defamation lawsuit against opposition leader Sam Rainsy on Wednesday, keeping up pressure ahead of elections.

President of the Cambodian People's Party (CPP) and Prime Minister Hun Sen greets during a ceremony at the party headquarters to mark the 38th anniversary of the toppling of Pol Pot's Khmer Rouge regime in Phnom Penh, January 7, 2017. REUTERS/Samrang Pring TPX IMAGES OF THE DAY - RTX2XU5X

Political tension has been growing in the Southeast Asian country ahead of local elections this year and a general election next year, in which Hun Sen’s three-decade grip on power will be challenged.

Sam Rainsy lives in exile in France and was sentenced in absentia last month to five years in prison for posting a fake government pledge to dissolve the border with Vietnam.

The latest lawsuit against Sam Rainsy, in the Phnom Penh Municipal Court, accuses him of defamation over claims made in France that the prime minister bribed an activist to break up the opposition Cambodia National Rescue Party.

“What Sam Rainsy did was an act of distorting truth, affecting the prime minister’s reputation,” said Ky Tech, Hun Sen’s lawyer.

Responding to the accusation, Rainsy said on Twitter he welcomed lawsuits with Cambodia’s “kangaroo court”.

“Its discussion means more publicity for Hun Sen’s shameful acts,” he said.

The activist, Thy Sovantha, also filed a suit against Rainsy for saying she had taken money from Hun Sen.

Opposition politicians accuse the authorities of intimidation ahead of the elections.

In the 2013 general election, the CNRP won 55 seats in the National Assembly, leaving Hun Sen’s Cambodian People’s Party with 68 in the 123-seat assembly.

The latest lawsuits were a sign of the ruling party’s concern over its election prospects, said Miguel Chanco, regional lead analyst of the Economist Intelligence Unit.

“The government is using every tool in the box to discredit and suppress the opposition,” Chanco said.