PHNOM PENH • Cambodian opposition leader Kem Sokha was arrested in a police raid on his home early yesterday as Prime Minister Hun Sen accused him of treason with the backing of the United States.

It marks an escalation in a campaign against any potential threats to Mr Hun Sen's hold on power ahead of an election next year at which Mr Kem Sokha, 64, has been expected to be his main challenger.

"It's an act of treason with conspiracy with a foreign country, betraying his own nation. This requires arrest," Mr Hun Sen told a group of garment workers, according to the pro-government Fresh News website. The premier, 65, said of the alleged foreign third party: "It's the United States."

Mr Kem Sokha has led the main opposition Cambodia National Rescue Party since his predecessor resigned in February. Pictures in Cambodian media showed Mr Kem Sokha being led away with his hands behind his back.

The government released a video on its Facebook page in which Mr Kem Sokha appeared to tell a group of supporters about a strategy to win power which he said had the support of "the Americans", rather than an immediate plot to topple Mr Hun Sen. In the video, which the government said was shot in Australia, Mr Kem Sokha said the Americans had hired academics to advise on a strategy to change Cambodia's leaders. "And if I follow such a tactic and strategy and if I could not win, I do not know what else to do."

The opposition made no immediate comment on the veracity or content of the video. If Mr Kem Sokha is found guilty of any offence, it could allow the government to shut the party down under a new law that forbids political parties from having a leader who has been convicted.

Mr Kem Sokha's daughter Monovithya Kem said her father was taken away handcuffed after a raid by between 100 and 200 policemen without an arrest warrant. She said his whereabouts was unknown.

REUTERS, AGENCE FRANCE-PRESSE