Protesters threw rocks at police who fired at least 10 teargas canisters near Phnom Penh's Royal Palace, where witnesses said supporters of Cambodia's main opposition party had tried to removed razor-wire barricades.
The clash came amid tension heightened by the discovery of a bomb and some grenades around the city on Friday and risk escalating a six-week standoff that has become one of the biggest tests of Prime Minister Hun Sen's three decades in power.
His Cambodian People's Party (CPP) won the election with 68 seats to the Cambodia National Rescue Party's 55.
His greatly reduced majority that signals dissatisfaction with his rule despite rapid economic growth in a country that for decades was seen as a failed state. But the Cambodia National Rescue Party (CNRP) and its supporters insist they won the July 28 vote and yesterday held their second mass rally in eight days to demand an independent investigation into their complaints of vote fraud.
The government has refused to allow that.
"Our vote is our life," CNRP's deputy president, Kem Sokha, told about 20,000 supporters at Freedom Park, where the protest took place.
"They stole our votes, it's like stealing our lives."
The clashes left several people with minor wounds but raised tension to a new level. Police threatened legal action and put razor-wire fences and fire trucks across several roads.