Supporters of the opposition Cambodia National Rescue Party rode motor scooters through Phnom Penh, many adorned with placards that called for Prime Minister Hun Sen to step down.
USAID has provided about $5 million to the organization in five different provinces.
Burma joined Asean in 1997 but its isolation from the international community and image as a pariah state prevented it from hosting Asean in 2006.
Interior Ministry spokesman Khieu Sopheak said the demonstrations have not crossed any lines, but if they become a threat to the government, they will be broken up by force.
Official election results gave 68 of 123 seats to the CPP, with the remainder to the opposition.
Kem Sokha, vice president of the Cambodia National Rescue Party, said the government is harming its citizens and will face “people power” as a result.
The rally was the second day in a row that opposition supporters gathered to demand a credible investigation into allegations of election fraud or to demand another election.
The 62-page report found that Identity Certificates for Elections, which are temporary documents for voters, were issued to up to 20 percent of eligible voters by election authorities.
Brad Adams, Asia director for Human Rights Watch, called Hun Sen’s promises of improved rights in the country “the same old song.”
Tens of thousands of South Africans gathered Tuesday to bid farewell to anti-apartheid icon Nelson Mandela.
The people of the 21st Century are very fortunate to have had the influence of Nelson Mandela, a former ambassador says.
Authorities say they are looking into an alleged threat made to an opposition official over Facebook.