BBC correspondent in Phnom Penh

The formal campaign for Cambodia's general elections on July 27 is still several months away, but if election violence is any measure, the contest is already started.

The latest killing, that of Om Radsady, an adviser to the royalist Funcinpec party, has left many Cambodians stunned and fearful.

The Interior ministry says that Om Radsady was killed for his mobilephone.

But Peter Leuprecht the United Nations human rights envoy in Cambodia,says it was an assassination and possibly a sign of escalating election violence.

He warned the country's National Election Committee against being a paper tiger, urging the committee to penalise those responsible.

"I sincerely hope that this trend of killings before elections will atlast discontinue in Cambodia and I sincerely hope that the authorities will do everything in their power to prevent such acts of violence.

"If, nevertheless, such acts occur, the law must be applied and thesecases must be seriously investigated, and those responsible must be punished,"he said.

Statements about what should be done mean little on the streets of Cambodia, where renewed tension stems from the latest killing and from anti-Thai riots in January which are widely seen to have been orchestrated for political purposes.

The National Election Committee is around the corner from the Thaiembassy, which was burned and smashed by rioters angered by reported claims over their ancestral heritage at the temples of Angkor.

The NEC's chairman, Im Sousedy, told the BBC that he was still waiting for the government to explain if there were political motivations behind the violence.

Bangkok has demanded almost $50m dollars in compensation.

Some say Cambodians have learnt a rare lesson of responsibility from the riots.

Impunity

But, according to human rights activist Thun Saray, it is just a blip in a deeply-rooted culture of impunity, where violence and power are natural partners.[