By Prak Chan Thul
PHNOM PENH (Reuters) - Cambodia's parliament voted on Monday to allow the prosecution of opposition leader Kem Sokha on treason charges that have been criticized by Western countries and are dismissed by his party as nonsense.
Kem Sokha's arrest on Sept. 3 marked an escalation in a crackdown on critics of Prime Minister Hun Sen ahead of an election next year in which he could face the toughest electoral challenge of more than three decades in power.
Kem Sokha's Cambodian National Rescue Party (CNRP) boycotted the parliamentary vote, but it passed easily because Hun Sen's Cambodian People's Party (CPP) has a majority. The vote was passed with 67 out of 123 voting in favor. None opposed it.
The vote was specifically on whether to prosecute Kem Sokha and it was unclear what it meant for the status of the parliamentary immunity from prosecution that he technically gets as an elected member of parliament.
The evidence presented against Kem Sokha so far is a video recorded in 2013 in which he discusses a strategy to win power with the help of unspecified Americans. His lawyers have dismissed the evidence as nonsense and said he was only discussing election strategy.
National Assembly President Heng Samrin said the vote allowed the government "to proceed with the case of arresting, detaining and charging Kem Sokha."
Parliamentarians from the opposition party said they would go to the prison where Kem Sokha is being held to demand his release. Security was increased at the prison, several hours drive from the capital Phnom Penh near the border with Vietnam.
Hun Sen, a 65-year-old former Khmer Rouge commander, has ruled Cambodia for more than 30 years and said last week that he planned to stay in power for another decade.
Western countries and human rights groups have raised doubts as to whether next year's election can be fair after the arrest of Kem Sokha and a crackdown on the opposition, activists and independent media. But Hun Sen has support from his main ally, China.
(Writing by Matthew Tostevin; Editing by Simon Cameron-Moore)