* Clashes, major test for PM's long rule
* Opposition claims electoral fraud denied it victory
* One man reported shot dead, several injured
Cambodian Prime Minister Hun Sen met the country's main opposition leader on Monday after violence broke out at a rally the previous day to protest July's contested general election result and one man was shot dead.
At least 1,000 protesters were camped out in the rain in makeshift tents in Freedom Park in the capital Phnom Penh late on Sunday and many remained on Monday in a tense standoff.
The electoral authorities say Hun Sen's Cambodian People's Party (CPP), which has been in power for 28 years, won the election, but the opposition claims the CPP rigged the vote and wants an independent inquiry.
Clashes broke out in several places in Phnom Penh on Sunday as supporters of the opposition Cambodia National Rescue Party (CNRP) tried to remove razor-wire barricades and refused to restrict their protest to a designated site in Freedom Park.
Chan Soveth, a worker for human rights group Adhoc, said a man was shot in the head and died when CNRP supporters tried to move razor-wire barricades set up by the authorities in the Monivong Bridge area near their party headquarters.
He said the man was not a political protester but someone who lived in the area and was among a group of local residents angry that they could not reach their homes.
Chan Soveth said he had visited five other people in hospital who had been hit by live rounds. "These bullets came from where the authorities were," he told Reuters.
Kheng Tito, National Military Police spokesman, said police had used only teargas, batons and smoke grenades and he could not say how the man died.
"I don't know how he was killed. We didn't use live bullets," he said.
The capital has been tense since the election on July 28 but protests were mostly calm until this weekend and the security forces, prone to cracking down on dissent in the past, had also been restrained.
King Norodom Sihamoni summoned Hun Sen and CNRP leader Sam Rainsy to a meeting on Saturday morning but it lasted just 30 minutes and apparently produced no results.
According to the electoral authorities the CPP won the election with 68 seats to the CNRP's 55, a greatly reduced majority that, even before the protests, signalled dissatisfaction with Hun Sen's authoritarian rule despite rapid economic growth in a country seen for decades as a basket case.
The CNRP says it was cheated out of 2.3 million votes that would have handed it victory.
It was unclear how long the demonstration against Hun Sen would last. Those wrapped in blankets in Freedom Park have vowed to stay for at least three days.
"We're here to protest against the National Election Commission that stole our votes. They should be the referee, not the puppet of the ruling CPP," said Yong Ol, 43, who had come to the capital by truck from southern Prey Veng province.
Analysts see the standoff as a war of attrition stacked in favour of a premier not known for compromise.
The opposition will try to paralyse the legislature by boycotting parliament's first session on Sept. 23.
Hun Sen, 61, has been a dominant force in Cambodia for years and has taken credit for steering it away from a chaotic past towards economic growth and development.
But many urban youth born after the 1975-1979 "Killing Fields" rule of the Khmer Rouge see little appeal in his iron-fisted approach and are disillusioned by growing land evictions, labour disputes and graft plus the country's close political ties with top investor China.