The United Nations Secretary General, Ban Ki Moon, says the UN will replace all the officials who were involved in fraudulent procedures in Afghanistan's presidential election in August.
Afghan people will return to the polls on 7 November for a new round of voting.
Ban ki Moon told the BBC the UN would take several measures to make the second round of presidential elections more fair and transparent.
He said it would try to replace 200 top officials out of 400 electoral districts, either because they did not follow correct procedures or because they were complicit in fraud.
The secretary general defended the UN's role in organising what turned out to be a massively fraudulent election.
He blamed the widespread cheating on a young, or what he called an immature democracy.
He also dismissed charges that the UN tried to cover up the extent of the fraud, saying the issue had been not to hide it, but how best to deal with it.
Run-off election set
After weeks of mounting international pressure, President Hamid Karzai agreed to the run-off against Dr Abdullah Abdullah.
The announcement came a day after a United Nations panel said it had found clear evidence of fraud in the first round, meaning Mr Karzai did not win enough votes to secure an outright win.
The elections were held on 20 August. Initial results suggested Mr Karzai received 55% of the vote and Dr Abdullah 28%.
However, the Electoral Complaints Commission ordered that ballots from 210 polling stations be discounted.
This meant Mr Karzai's total was reduced to below the 50% plus one vote threshold for outright victory, indicating a second round was needed.
Mr Karzai was previously reluctant to accept that a second vote was required. However, he told a news conference on Tuesday that he accepted the findings, adding they were a "step forward" for democracy.
Dr Abdullah also said the move would "help democracy in this country and strengthen the faith of the people in the democratic process".
The BBC reports US Senator John Kerry played a pivotal role in persuading President Karzai to accept the need for a second round.
Mr Karzai's decision was warmly welcomed by world leaders.
US President Barack Obama described it as an important and constructive step forward.
British Prime Minister Gordon Brown also welcomed President Karzai's "statesmanlike" acceptance of the run-off.