They said the man - from the party headed Sam Rainsy - had been found after being abducted by unidentified armed men.

Earlier, Mr Rainsy, one of the country's foremost opposition leaders, said his party was withdrawing from the general election, which he described as leading to a farce.

His criticisms included allegations of intimidation by supporters of Cambodia's second prime minister, Hun Sen.

Earlier this week, officials of the Funcinpec Party of the ousted co-prime minister, Prince Norodom Ranariddh, said two of their members had been shot dead.

'Result known'

Hun Sen: refuses to delay

Mr Rainsy told the BBC that his party did not want to endorse any election where the result was known in advance.

His comments are the latest in a series of complaints by opposition parties and local human rights groups that Cambodia's second prime minister, Hun Sen, has tried to control the election process by restricting basic freedoms.

Mr Rainsy said several hundred thousand Cambodians had been prevented from registering to vote and that the opposition parties were not being given fair access to the media.

He urged Western countries which give aid to Cambodia to withdraw their support unless the government agrees to delay the election until conditions for a fairer poll can be created.

Mr Rainsy's comments were supported earlier on Friday by two international groups which have been monitoring preparations for the election. They also called for the polls to be delayed, saying the political atmosphere was characterised by intimidation.

The organisations, Human Rights Watch Asia and the International Crisis Group, warned that if opposition groups lost faith in Cambodia's democratic process, the chance of a return to civil war would increase.

The BBC Cambodia correspondent says the response of leading powers such as Japan, the United States and the European Union is now crucial.

Meanwhile, Cambodia's second prime minister, and de facto leader, Hun Sen, has maintained that the election has been free and fair despite a recent increase in attacks on opposition supporters.

He has repeatedly brushed-off complaints and refused to consider any postponement of the polls.