Cambodia's opposition leader is touring Southeast Asia to appeal for the intervention of neighbouring countries in a political stalemate triggered by disputed elections, his party said Tuesday.

Sam Rainsy, whose opposition Cambodia National Rescue Party (CNRP) is boycotting parliament over the controversial July polls, left on Monday evening for countries including Singapore and the Philippines.

"His goal is to meet the leaders of some countries in order to seek their intervention in the election irregularities," party spokesman Yem Ponharith told AFP.

"If neccessary he may continue to Europe, otherwise he will return to attend a rally on October 6," the spokesman added.

Cambodia's parliament last week approved a new five-year term for Hun Sen following weeks of political turmoil.

The CNRP denounced what it described as a "constitutional coup" after the legislature -- with only ruling party MPs in attendance -- extended Hun Sen's nearly three decades in power.

The opposition, which is demanding an independent probe into alleged electoral fraud, has said it will hold another mass demonstration on October 23.

Tens of thousands of opposition supporters joined three days of rallies in the capital last month that turned bloody.

One protester was shot dead and several wounded as security forces clashed with a stone-throwing crowd.

Hun Sen -- a 61-year-old former Khmer Rouge cadre who defected and oversaw Cambodia's rise from the ashes of war -- has ruled for 28 years and vowed to continue until he is 74.

Rainsy returned from self-imposed exile in July after a royal pardon for criminal convictions which he contends were politically motivated. But he was barred from standing in the polls later that month.