Opposition leader Sam Rainsy offered money to voters who could help him prove Sunday's elections were rigged, as he led a rally at his party headquarters in the capital Wednesday.
More than 300 people gathered at the headquarters, under the watch of a large number of armed intervention, military and traffic police, who also positioned a water-cannon on Sotheros Boulevard outside the headquarters.
The Sam Rainsy Party won 26 seats in Sunday's election, according to National Election Committee preliminary figures, but he has contested the results.
Sam Rainsy said at the rally he was attempting to collect from voters proof they had used an illegal administrative form, No. 1018, for voting. He offered $50 to anyone who could prove they voted with the form, even though their names were not on the voter registry.
Opposition votes were taken by NEC "bandits," who conspired to ensure a Cambodian People's Party victory, Sam Rainsy said.
NEC Secretary-General Tep Nitha said the national election body had issued form No. 1018 a day before the election to people who were on voter registries but did not have photo identification, which is legal under election regulations.
Suth Dyna, deputy secretary-general of the Norodom Ranariddh Party, said Wednesday his party supported the Sam Rainsy Party's call for form 1018. His party was also preparing documentation to complain over election results, he said.