The government ban was criticised by local human rights groups and Amnesty International, which called on authorities Saturday ''to end their suppression of human rights and fully respect the right to peaceful assembly.''
Last week, opposition leader Sam Rainsy said his party planned to ignore a government ban and meet with supporters at Phnom Penh's Freedom Park. It was the first planned opposition assembly since authorities enforced a ban on public demonstrations in January after a spasm of political violence.
''We are determined to do whatever we can to achieve justice for the Cambodian people,'' Mr Rainsy said Sunday before the march at a Buddhist ceremony for victims of a grenade attack at a March 30, 1997, opposition rally that left at least 16 people dead and more than 100 injured. No one has ever been prosecuted for the attack.
''As long as I am still breathing, I will do everything I can to seek justice for the victims,'' Rainsy said.
Mr Rainsy had announced last week that he would meet supporters at the park, following the Buddhist ceremony, to discuss a breakdown of talks with the government on the appointment of a special commission for electoral reform. He described it as a ''people's congress'' to solicit the opinions of some 5,000 party members on what the opposition should do.
Instead, Mr Rainsy marched with about 500 opposition supporters to the party's headquarters.
The Cambodia National Rescue Party is challenging the results of a general election last July that they allege was rigged by Prime Minister Hun Sen's ruling party. Their protests demanding that Hun Sen step down and call new elections peaked late last year.