* Critics say Hun Sen seeking to silence opposition ahead of 2018 poll
* Western countries criticise arrest of opposition leader
* In power for 32 years, Hun Sen's main ally is China
Cambodian government lawyers filed a lawsuit on Friday to demand the dissolution of the main opposition party, in a move that would help Prime Minister Hun Sen extend his 32-year rule when the poor Southeast Asian nation votes in an election next year.
The attempt to disband the Cambodia National Rescue Party (CNRP) comes after its leader, Kem Sokha, was charged with treason following his arrest on Sept.3.
In their lawsuit on Friday, government lawyers said the opposition had conspired with foreigners to topple the government, citing a 2013 video clip that shows Kem Sokha talking about a plan to take power with the help of Americans.
"Today we filed a lawsuit at the Supreme Court on behalf of the Interior Ministry to ask to dissolve the CNRP," Ky Tech, one of the government lawyers, told reporters.
"The CNRP, besides colluding secretly with foreigners ... also intends to serve foreigners," the lawsuit said.
The U.S. embassy in Phnom Penh has rejected the accusations and Kem Sokha's arrest was condemned by Western countries, who have questioned whether next year's election can be fair following the crackdown on opposition leaders, activists and journalists.
Hun Sen, a former Khmer Rouge commander who defected from the genocidal group and helped drive it from power in 1979, is allied to China, and Beijing says it supports the Cambodian government's efforts to maintain national security and stability.
Half of Cambodia's opposition members of parliament have fled the country. One of the remaining parliamentarians derided allegations that the CNRP had been involved in planning a US-backed coup.
"This is intended to destroy democracy in Cambodia," Mao Monyvann said of the move to shut down the CNRP.
The ruling Cambodian People's Party narrowly won the last election in 2013 after losing seats to the opposition in what was Hun Sen's worst election result since Cambodia returned to full democracy in 1998.
The ruling party lost ground in local elections in June, after which, according to opposition members, Hun Sen stepped up a campaign against dissenting voices.
