Sam Rainsy (File photo)

Cambodia's legislature has stripped opposition leader Sam Rainsy of his parliamentary immunity on Thursday, leaving him vulnerable to prosecution for defaming Prime Minister Hun Sen. Mr. Rainsy has left the country fearing arrest.

Dozens of armed forces surrounded the National Assembly building in Phnom Penh on Thursday, as lawmakers inside voted to remove the immunity of Sam Rainsy and two other opposition politicians.

Assembly members are normally exempt from legal prosecution or arrest for opinions expressed while fulfilling their duties. But a two-thirds legislative vote can revoke the safeguard.

The move Thursday now leaves the opposition leader open to prosecution.

Sam Rainsy faces a defamation suit by Prime Minister Hun Sen after Mr. Rainsy accused the government of planning to kill political opponents. The governing coalition partner and head of the National Assembly, Prince Norodom Ranariddh, is also suing Sam Rainsy for libel for alleging he accepted bribes to join the coalition last July.

Mr. Rainsy, who said he had feared arrest, left Cambodia Thursday and is now staying outside Bangkok, Thailand.

His party's spokesman, Ung Bun Ang, says Mr. Rainsy wants to draw international attention to the situation.

"It seems to me that this is really a sad day for democracy in Cambodia as the ruling party is prepared to do anything to shut down the opposition in Cambodia. So that means that our suffering will continue and we need to be stronger and stronger to handle, to manage the situation," he said.

The United States Embassy in Phnom Penh immediately condemned Cambodia's legislature, calling its action a major setback for democracy. In a written statement the embassy, says stripping Mr. Rainsy's immunity appears to be aimed at silencing dissent.

War-torn Cambodia has maintained relative stability since 1997, when Hun Sen seized power from his then co-prime minister, Prince Norodom Ranariddh. Political deadlock gripped Cambodia after the last elections failed to produce a majority government. It took 11 months for Prime Minister Hun Sen to get a coalition agreement with the prince's party, leaving the Sam Rainsy party the only effective opposition.