PHNOM PENH, Cambodia -- Cambodia's opposition appeared to make impressive gains in Sunday's general election, though the ruling party claimed a victory that would extend the mandate of longtime Prime Minister Hun Sen. The results, if confirmed, lend support to opposition contentions that the vote could usher in opportunities for greater democracy.

Khieu Kanharith, a spokesman for the ruling Cambodian People's Party, said on his Facebook page that his party won 68 of the 123 National Assembly seats. He said the opposition Cambodia National Rescue Party won 55 seats -- gaining heavily on the 29 it held in the outgoing parliament.

The opposition party was reserving its projections of the size of its gains pending the release of more figures. But even the 55 seats conceded by the ruling party represented a stunning upsurge in fortune for the CNRP, which had predicted extensive vote-rigging.

Opposition leader Sam Rainsy -- who returned to Cambodia this month from years in self-imposed exile -- said in a statement that it was a "historic day," but urged his supporters to maintain calm and wait for official results to be released.

Provisional results from the official National Election Committee were being announced Sunday night on state television, but only by individual polling stations, making it impossible to get an immediate overview of the count. It was not clear when final official tallies would be announced.

If the results stand as the ruling party projected, it would be a huge boost for the much beleaguered opposition, giving it a strong platform for future growth. However, a simple majority is sufficient for most legislative business, ensuring that the CPP can continue to administer the country much as it wishes, though with increased sensitivity for public opinion. The CPP has an overwhelming majority of local administration posts as well.

Rainsy had said Saturday that while his party could not expect victory with the deck stacked against it, the election would represent a break with the past and a chance to work for "truly free and fair elections."

Hun Sen has been in power for 28 years and says he has no intention of stepping down soon. His authoritarian rule has given him a stranglehold over the state bureaucracy that makes challenges to his authority difficult to mount.

The general election was Cambodia's fifth since 1993, when the United Nations helped stage the country's first free polls since the 1975-79 genocidal rule of the Khmer Rouge and a subsequent period of civil war and one-party rule.

A pressing question is how Hun Sen will react if the opposition has in fact made such significant gains. Mercurial in temperament, historically he has accepted neither defeat nor victory with good grace.

After his party ran second in 1993, Hun Sen insisted on being named co-prime minister, then ousted his partner in government four years later in a bloody coup. After election victories in later years, he showed a pattern of cracking down on critics.

The streets around Hun Sen's residence in Phnom Penh, the capital, were closed Sunday, with security personnel patrolling in an apparent effort to ward off any protesters.

Hun Sen, 60, has a reputation as a tough and wily survivor, starting with his defection from the Khmer Rouge to Vietnam, which after invading to oust the radical regime installed him first as foreign minister and later as prime minister.

Rainsy, 64, has long been the thorn in Hun Sen's side. He spent the Khmer Rouge years in France, where he was educated in economics and political science. As a member of a royalist party, he served as finance minister in the government elected in 1993, but was kicked out from his party and his post for his outspoken anti-corruption stand.

Rainsy founded his own party in 1995, and two years later narrowly escaped being killed in a grenade attack on a rally he was leading. The perpetrators were never brought to justice but were suspected of being linked to Hun Sen's bodyguards.

Despite his party's good showing Sunday, Rainsy will be in a state of political limbo. He was not allowed to run as a candidate or even vote in the election, because he missed the registration deadlines as he stayed abroad for almost four years to avoid a jail term for convictions that he said were politically motivated. He returned July 19 only after receiving a royal pardon at the behest of Hun Sen, his longtime and bitter rival.

The pardon was an evident effort by Hun Sen to appease critics of the election process, including the United States, who suggested that Rainsy's exclusion was a major sign that the polls would not be free and fair.

Critics alleged that the process was heavily rigged anyway. Rainsy's party and nonpartisan groups charged that the ruling party used the machinery of government and security forces in an unfair manner to reward or pressure voters.

They also said that voter registration procedures were badly flawed, possibly leaving more than 1 million people disenfranchised. The independent Committee for Free and Fair Elections said Saturday that the ink with which voters were supposed to stain their fingers to prevent them from voting twice was not indelible as claimed.

The extent of voting irregularities was not clear Sunday, despite many anecdotal accounts spread on social media such as Twitter

Hun Sen's party and the government-appointed National Election Committee said the election process was fair.

Despite its showing, the opposition CNRP was not in a conciliatory mood.

Rainsy's wife, Tioulong Saumura, a candidate in Phnom Penh, said she did not accept the ruling party's figures. Asked if she thought the CNRP won more than 55 seats, she replied: "Of course. Almost everywhere we lead. No way we have 55 and they have 68."

Rainsy had issued a statement early Sunday evening claiming victory, but later retracted it.

CNRP spokesman Yem Ponhearith said late Sunday that the party was still collecting results and would announce its tally when it was done.

"I can say that so far the number of seats is very close between the two parties," he said. "At the moment we appeal to the people to be patient and wait for the final data we are collecting from the provinces."

Voters appeared to be happy just to cast their ballots.

"I am delighted that today that I able to express my voice through the ballot paper. I've voted for the party that I love," said 25-year-old Reth Sonitha.

Cambodia has 9.7 million registered voters in a population of almost 15 million. The major portion of the electorate is under 30 years old.

The election campaign was not marked by the kind of violence, including killings, that plagued past polls.