By Prak Chan Thul
PHNOM PENH (Reuters) - Thousands of demonstrators defied road blocks and a jail threat to hold a march in Cambodia's capital on Sunday in a last-gasp push for an independent probe into a July election they say was fixed to favor the ruling party.
Supporters of the opposition Cambodia National Rescue Party (CNRP) ignored a government order to stay off the streets and denounced the victory by allies of Prime Minister Hun Sen, who now faces one of his biggest tests of three decades in power.
His Cambodian People's Party (CPP) won the election with 68 seats to CNRP's 55, a greatly reduced majority that signals dissatisfaction with his rule despite rapid economic growth in a country that for decades was seen as a failed state.
Riot police stood by as politicians, activists, factory workers and Buddhist monks broke off from the march chanting "change, change" as they cut through side streets to avoid a route blocked off by fire trucks and razor-wire fences.
The march comes amid a deepening political standoff and tension heightened by Friday's discovery of a home-made bomb near parliament and hand grenades close to Freedom Park, the site of Sunday's mass rally, the CNRP's second in eight days. About 20,000 demonstrators attended.
"Our vote is our life," CNRP's deputy president, Kem Sokha, told supporters. "They stole our votes, it's like stealing our lives."
King Norodom Sihamoni invited Hun Sen and CNRP leader Sam Rainsy to his palace on Saturday to try to end the deadlock, but the meeting ended after 30 minutes with no breakthrough.
CNRP says it will try to paralyze the legislature by boycotting parliament when it holds its first session on September 23, arguing that it was cheated of 2.3 million votes to keep CPP in office for another five years.
It is refusing to give up until the government agrees to let outsiders conduct an investigation, but the opposition is fast running out of options.
The government and the National Election Commission, which Rainsy accuses of collusion, are both standing by the official result and the Constitutional Council ruled on Friday that all allegations of foul play had been investigated already and no new probe was needed.
Thousands of riot police armed with batons and shields have been running crowd control drills in recent weeks.
Many Cambodians fear the protest could prompt a tough response by security forces with a reputation for cracking down hard on disgruntled factory workers and victims of land evictions.
Hun Sen, 61, has taken credit for steering Cambodia away from its chaotic past towards economic growth and development, but many urban youth born after Khmer Rouge "Killing Fields" reign of terror from 1975-1979 see little appeal in his iron-fisted approach.
Hun Sen and CPP are not known for compromising on either domestic or international disputes and few people expect the government to bow to pressure this time either.
"The CPP won't agree to anything we demand," said CNRP supporter Ngor Lay from southern Kandal province. "They just love power and they have the courts in their hands."
(Writing by Martin Petty; Editing by Nick Macfie)