The government of Cambodia has taken the first legal steps seeking to disband the country's main opposition party, the latest in a series of moves that would help it gain an advantage ahead of a general election next year.

The interior ministry on Friday filed a lawsuit with the Supreme Court asking for the Cambodia National Rescue Party (CNRP) to be dissolved on the ground that it was involved in a plot to topple the government, said spokesperson Khieu Sopheak.

The CNRP is the only party aside from the ruling Cambodian People's Party with representatives in parliament, and no third political grouping comes close in terms of popularity and support. The opposition posed an unexpectedly strong challenge in 2013's general election, and the government has since taken steps to tighten its grip on power.

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Khieu Sopheak said the government had received "21 pieces of concrete evidence to prove that the opposition party has intentionally sought to topple the government through a 'colour revolution'" - a term used to describe movements to replace governments in a number of countries.

The attempt to disband the CNRP comes after its leader, Kem Sokha, was charged with treason following his arrest on September 3. He could face up to 30 years in prison.

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.

The opposition party has denied the treason allegation, saying the charge is politically motivated. Many senior CNRP leaders have since fled the country, fearing arrest.

One of the remaining opposition MPs 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.

Western countries have condemned the opposition leader's arrest, and have questioned whether next year's election can be fair following the crackdown on opposition leaders, activists and journalists.

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Hun Sen, prime minister of Cambodia and 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.

The Cambodian People's Party narrowly won the last election four years ago 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.

Phil Robertson, deputy director of Human Rights Watch's Asia division, criticised the international community for not responding more strongly to Hun Sen's crackdown.

"The international community obligated itself to protect human rights and democracy in Cambodia when they signed the Paris Peace Accords, but now they are looking the other way as that dream dies," Robertson told Reuters news agency.

"Prime Minister Hun Sen is effectively putting an end to Cambodian democracy," he said.

An English-language newspaper, The Cambodia Daily, was shut down after being accused of not paying a huge tax bill - an assessment it strongly disputed. More than a dozen radio stations that broadcast dissident voices or used programming from US government-funded Voice of America and Radio Free Asia were forced to stop broadcasting for alleged breach of regulations.