Cambodia's opposition party on Wednesday appealed against preliminary official election results that handed a narrow victory to strongman Prime Minister Hun Sen despite allegations of widespread fraud.

The results, released Monday by the National Election Committee (NEC), found the incumbent premier's long-ruling Cambodian People's Party (CPP) had edged the hotly disputed election, taking 3.2 million votes to the opposition's 2.9 million.

The Cambodia National Rescue Party (CNRP) has rejected the results, demanding an independent probe into its allegation that the election was tarnished by massive vote-rigging.

Party officials lodged a complaint with the NEC on Wednesday.

"We are demanding that the NEC reviews its mechanisms and processes," senior opposition official Kuy Bunroeun told reporters.

"The CNRP cannot accept the results," he said, adding they were "far different" from his party's tally that shows it won the election with an estimate of 63 seats in parliament.

Cambodia has been stuck in a political impasse since the CPP claimed victory in the July 28 vote, with the military deployed in the capital Phnom Penh last week after the opposition threatened mass demonstrations.

The final results giving the number of seats won should have been released later this week, but the NEC said the political deadlock means they will now be announced by September 8.

"Due to the complaints (from CNRP), the release of the final results will be delayed," NEC's secretary-general Tep Nytha told AFP.

The CPP claims it secured an estimated 68 of the 123 lower house seats available, losing 22 seats since the last polls. The CNRP was said to have won 55.

If confirmed, it would be the ruling party's worst election result since 1998.

The opposition, which has threatened to boycott parliament, last week called on the UN to help resolve the dispute to protect "the victory" of the people.

While an inquiry into the election has been broadly accepted by all involved, the parties have failed to agree on the terms, particularly over a mooted role for the United Nations.

Hun Sen -- who has been in power for 28 years -- has vowed to establish a government under his leadership despite the opposition's allegations.

The premier, 61, a former Khmer Rouge cadre who defected from the murderous regime, has vowed to rule until he is 74.

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