The President of the Son Sann party, Son Soubert, told reporters in Phnom Penh that his party and that of the former finance minister, Sam Rainsy, would continue campaigning for the time being.

"We will continue to stay in but we reserve the right to withdraw if there is violence," he said.

Sam Rainsy: set to contest poll for now

The parties set a deadline of July 5 to decide whether to boycott the poll. That date coincides with the first anniversary of the coup in which the First Prime Minister, Prince Norodom Ranariddh was forcibly removed by co-premier Hun Sen.

Both opposition parties have accused members of Hun Sen's Cambodian People's Party of using violence and intimidation against opposition supporters in the run-up to the vote on July 26.

In a joint statement they said they could not be sure that conditions for the election would improve or that the result of a free and fair poll would be respected.

They called on the international community to step up pressure on the ruling party to ensure Cambodian people were allowed to express their will freely.

Human rights abuses

Prince Ranariddh's Funcinpec party marked the anniversary of the coup by lamenting that no-one had been brought to justice for human rights abuses committed during the coup by forces loyal to Hun Sen.

Scores of the prince's supporters were executed following his overthrow. The United Nations and human rights groups have criticised Hun Sen's government for not investigating the killings.

Hun Sen: says he is not "a monster"

In a statement Funcinpec said that the failure to bring human rights offenders to justice undermined the fairness of the upcoming elections.

It also attacked the international community for not pushing the government harder on the matter.

"Regrettably, certain countries which used to be the pillars of freedom, human rights and democracy have done nothing to urge Hun Sen to bring to justice those responsible for the extra-judicial killings," it said.