Update 10:30 a.m. EDT: The Cambodian Peoples Party of Prime Minister Hun Sen claimed victory in Sunday's election, Reuters reports, but with a much-reduced majority in Parliament.
Information Minister Khieu Kanharith said on his Facebook page the final count was 68 seats for the CPP and 55 for the opposition Cambodia National Rescue Party, down from 90 for the CPP in the previous Parliament.
The National Election Committee has not published figures but was expected to give a partial count later in the day. CNRP leader Sam Rainsy said earlier his party had won the election but then withdrew the statement. No explanation was given.
While not formally accepting defeat, Rainsy was conciliatory and called for calm, Reuters reported.
"We want to thank all Cambodian people ... regardless of their political affiliation, Cambodians who support all political parties, for their dignified participation in this election, for their contribution to make democracy move forward," he told a news briefing. He appealed to his youthful supporters not to cause any trouble: "We call for peace and reconciliation."
Cambodia's opposition claimed an upset victory Sunday in an election the long-ruling party of Prime Minister Hun Sen had expect to win easily, the Associated Press reports.
Sam Rainsy, leader of the Cambodia National Rescue Party, said in a brief emailed announcement that his party had won Sunday's general election, although no results had yet been released by the authorities.
There was no immediate reaction from the ruling Cambodian People's Party.
Earlier, Reuters reported that security was tightened in Phnom Penh Sunday after voting ended.
Military police blocked off a road leading to Hun Sen's home and one going to the offices of his CPP and the National Election Committee.
Eng Chhay Eang, a CNRP candidate, said that based on vote counts from some polling stations provided by party monitors, the CNRP was positive of gaining more seats. "At places where we were defeated last time, we are now taking the lead," he said.
Backed by a compliant media and with superior resources, the CPP is confident of victory, but analysts believe the recently united opposition may dent its majority. The CPP had 90 of the 123 seats in the outgoing parliament and the parties that united to form the CNRP had 29.
Voting, like the campaign itself, was generally peaceful although scuffles were reported in various places, mostly involving people complaining about irregularities. Angry voters set fire to a car outside one polling station in the capital and some smashed up police cars, Reuters reported.
The CNRP has alleged electoral lists were manipulated to give the CPP more votes and also complained about the disruption of meetings and campaigning by the security forces for Hun Sen.
"The partisanship of the military and police has created an intimidating atmosphere for voters in many parts of the country," U.S.-based Human Rights Watch said in a statement ahead of the poll.
More than 9.6 million people were eligible to vote. The National Election Committee could publish some provisional results on Sunday evening. Full results could take weeks.
Rainsy, a former finance minister, returned from exile after a royal pardon. He had faced a jail sentence handed down in 2010 for spreading disinformation and falsifying maps to contest a new border agreed with Vietnam, charges he called politically motivated.