The most senior United Nations official in Afghanistan today acknowledged that "widespread fraud" had marred Afghanistan's presidential election, but denied allegations from his sacked second-in-command that he had attempted to cover up evidence of cheating.

With days to go until the final result of the August election, Kai Eide, the head of the UN mission in Kabul, admitted there had been "significant fraud". He said that the claims made by Peter Galbraith, the American diplomat sacked earlier this month, had "affected the entire election process".

The report of a fraud investigation is due in the coming days, which will decide the final outcome of the voting that took place more than seven weeks ago.

A western diplomat said it was "on a knife edge" whether enough fraudulent votes would be removed from the preliminary result to trigger a potentially difficult second round.

Public and international faith in the election plunged to at an all time low after the fraud allegations and the UN attempted to bolster credibility in the process today by surrounding Eide with leading ambassadors at the stage-managed press event.

Although the US, British, French and German ambassadors joined Eide for his attempt to set the record straight, none of them spoke and UN officials prevented journalists from asking them questions.

Eide said their presence was a "sign of international support" for his approach. Galbraith had claimed that his former boss failed to stop polling stations from opening in areas that were too dangerous for monitors to visit.

Eide said that he had been backed in his decision keep as many polling stations open by the main western powers, who were anxious not to disenfranchise voters.

"We all understood that if we pre-emptively removed 1,200 polling centres we would prevent a large number of voters, primarily Pashtun, from voting."

He said that would have created "an important element of instability in the country".

The Norwegian diplomat also defended himself against allegations that he banned his staff from handing over evidence collected on polling day that showed that actual voter turnout was far lower than the reported result. Eide said that some of the information was not in a fit state to hand over to the relevant authorities.

"It was often second or third-hand information and some changed from day to day. It is important to me that when information is shared and provided by the UN it must have the level of solidity that can make it authoritative," he said, adding that it would have been a "conflict of interest" for the UN to act as an observer in an election it helped to run.

Western diplomats are anxious to shore up support for the poll as the Election Complaints Commission, a watchdog led by non-Afghan staff, prepares to unveil the results of an investigation it ordered into electoral fraud. Around 10% of the 3,498 ballot boxes regarded as suspicious have been inspected by election staff looking for signs of irregularities.