Thousands of Cambodians, many holding lotus flowers symbolising peace, have joined a mass protest in the capital Phnom Penh in a last-ditch bid to challenge the prime minister's disputed election win.
The election was very unjust. There were a lot irregularities that we cannot accept
Demonstrators on Saturday rallied against the contested poll win by Hun Sen's long-ruling Cambodian People's Party (CPP), aware that the final results due on Sunday will effectively close the opposition's legal options to appeal.
About 10,000 people had gathered in the city's Democracy Park before an expected speech by the leader of the opposition Cambodia National Rescue Party (CNRP).
Thousands of members of the security forces have been mobilised for the gathering, but were keeping a low profile.
The CNRP has alleged widespread vote rigging in July elections in which the CPP claimed victory.
The opposition has urged its supporters to avoid violence.
Cambodia's government has urged foreigners to stay away from the rally while the US and Australian embassies have also warned their citizens to avoid the protest.
"I came to demand justice. Our votes have been stolen... the victory of the people has been stolen," said Uy Sarouen, 54.
His comments were echoed by 29-year-old Chaing Chantara who said people wanted "real democracy".
"The election was very unjust. There were a lot irregularities that we cannot accept," he added, referring to alleged widespread voting fraud.
According to preliminary official results from the National Election Committee (NEC), the CPP won 3.2 million votes to the CNRP's 2.9 million.
The country's Constitutional Council said on Friday that it had reviewed the CNRP's complaints against the election results and had broadly rejected them.
"In general, we uphold the decisions of the NEC," council spokesman Uth Chhorn said.
The CNRP expressed dismay at the outcome and pledged to keep up the pressure.
"The NEC, the Constitutional Council and the CPP are all in the same basket. So they join hands to distort the will of the people. We cannot accept this," said the party spokesperson, Yim Sovann.
The opposition wants an independent investigation of the alleged vote fraud.
"The chances of the opposition succeeding in its demands are proportional to the number of supporters joining the demonstration," Cambodian independent political analyst Lao Mong Hay said ahead of the rally.
Hun Sen's ruling CPP said it would not be swayed by the size of the protest turnout.
"They cannot put pressure on us," said senior party member Cheam Yeap. "The winning party won't become hostage to the losing side."
Hun Sen, 61, a former Khmer Rouge fighter who defected and oversaw Cambodia's rise from the ashes of war, has pledged to rule until he is 74.
His government is regularly accused of ignoring human rights and suppressing political dissent.