KABUL: Afghan authorities Monday began a sample audit of suspect ballots cast in the controversial elections, officials said, as the country inched closer to a final decision on the next president.

Afghans went to the polls on August 20 to elect their president for the next five years, but allegations of widespread fraud -- mainly directed against the incumbent Hamid Karzai -- have delayed the announcement of a winner.

Karzai leads the preliminary results with around 55 percent of the vote. He needs 50 percent plus one vote to be declared the winner.

His main rival, Abdullah Abdullah, has around 28 percent and has been at the forefront of vote-rigging accusations against Karzai.

Pivotal to the final outcome is the result of the audit of just over 10 percent of 3,498 ballot boxes -- up from 3,063, an official said -- that have been returned to Kabul from polling stations across the country for checking.

Ballots in 358 boxes are being examined by auditors from the Independent Election Commission (IEC), officials said, adding that results would be extrapolated from the sample.

The audit is expected to take two days, after which the IEC and the Electoral Complaints Commission (ECC) must fulfil other formalities before a final result can be declared.

Zekria Barakzai, Afghanistan's deputy chief electoral officer, said the final result is not likely before the end of next week -- pushing the timetable at least a week beyond earlier statements.

He said that, following the audit, "how many votes are fraudulent will be deducted proportionally from all the candidates' votes" -- a process that would see the percentage of valid votes held by each candidates remain the same.

ECC commissioner Scott Worden said, however, that deductions would not be proportional.

The audit applied "statistically sound methodology" by breaking the sample into six categories, he said, and evidence of fraud in the sampled ballots would indicate the incidence of fraud in all votes in the same category.

The fraud accusations dogging the vote have dismayed leaders of the international community, which has supported and bankrolled the process as a step forward on Afghanistan's road to democracy.

The situation was compounded last week when Peter Galbraith, deputy to the UN's special envoy to Afghanistan, was sacked over disagreements with his boss, Kai Eide, over how to deal with the fraud.

Galbraith later said Eide had been biased in favour of Karzai.

In Sunday's Washington Post, Galbraith wrote: "As many as 30 percent of Karzai's votes were fraudulent, and lesser fraud was committed on behalf of other candidates.

"In several provinces, including Kandahar, four to 10 times as many votes were recorded as voters actually cast.

"The fraud has handed the Taliban its greatest strategic victory in eight years of fighting the United States and its Afghan partners."

Orzala Ashraf, an independent analyst affiliated with the Dutch NGO Inter-church Organisation for Development Cooperation, said the delay in the results had paralysed Afghanistan politically, economically and militarily.

"No matter who wins we will still be living with an extremely undesirable and corrupt government that needs fixing," she told AFP.

As the anniversary approaches of the October 7, 2001, US-led invasion that pushed the Taliban from power, the fight against the insurgency -- by more than 100,000 foreign troops under US and NATO command -- is intensifying.

This year is the deadliest in the eight-year war, with independent website icasualties.org, which keeps a running tally, putting troop deaths so far in 2009 at 399, including 239 Americans.