UNITED NATIONS (Reuters) - The United Nations on Sunday voiced alarm at the escalating political tensions in Cambodia, including attempted arrests of politicians, amid allegations from the opposition that Prime Minister Hun Sen’s ruling party is persecuting it.

Last week Hun Sen said Cambodia’s next election will be in July 2018. Meanwhile leaders of the opposition are facing legal charges they say are politically motivated to stop them challenging the veteran premier in the vote.

“The Secretary-General (Ban Ki-moon) is concerned about the escalating tensions between the ruling and opposition parties in Cambodia, particularly arrests or attempted arrests,” U.N. spokeswoman Devi Palanivelu said.

“A non-threatening environment of democratic dialogue is essential for political stability and a peaceful and prosperous society,” she added.

Long before the Southeast Asian nation goes to the ballot box, political tensions have risen. The last election in 2013 marked self-styled strongman Hun Sen’s toughest challenge in three decades of rule.

The opposition Cambodia National Rescue Party (CNRP), led by Hun Sen’s longtime foe Sam Rainsy, accused the ruling Cambodian People’s Party (CPP) of cheating its way to victory and boycotted parliament for a year.

Rainsy has been in exile since late 2015 to avoid jail on charges for which he had previously received a royal pardon.

His deputy, Kem Sokha, was cited on Friday for contempt of court after failing to appear on Thursday to hear charges for procurement of prostitution over a leaked recording of purported telephone conversation he had with a woman.

Sokha’s lawyer, Sam Sokong, dismissed the charge as baseless, saying his client had reasonable grounds not to appear in court.

The CNRP and a workers union on Friday threatened mass protests and a parliamentary boycott if Sokha is arrested.