The vote has been overshadowed by claims of mass electoral fraud
Afghanistan's Election Complaints Commission has ordered a number of recounts and audits of votes from last month's presidential election.
The UN-backed body warned that it had found "clear and convincing evidence of fraud", the AP news agency reported.
It came after a senior UN envoy called for a crackdown on irregularities, amid mounting concern over the election.
According to the most recent results, President Hamid Karzai was close to the threshold needed for an outright win.
The 20 August poll has been overshadowed by claims of mass fraud and ballot-box stuffing against all the main candidates.
US ambassador Karl Eikenberry met Mr Karzai on Monday night to discuss his concerns. It is not known how the Afghan leader responded.
AFGHAN POLL FRAUD
8 Sep: Poll complaints body orders some recounts nationwide
6 Sep: About 200,000 votes are quarantined by poll officials
3 Sep: Claims 30,000 fraudulent votes cast for Karzai in Kandahar
30 Aug: 2,000 fraud allegations are probed; 600 deemed serious
20 Aug: Election day and claims 80,000 ballots were filled out fradulently for Karzai in Ghazni
18 Aug: Ballot cards sold openly and voter bribes offered
On Tuesday, Kai Eide, the UN special representative to Afghanistan, called in a written statement for the poll authorities to ensure the final outcome faithfully reflected the will of Afghan voters.
Later, the Election Complaints Commission (ECC) told the BBC there should be a recount where any single candidate received more than 95% of valid votes, in any polling station where more than 100 votes were cast.
The body - which has been investigating hundreds of allegations of major poll fraud - also called for an audit in any polling station where 600 or more votes were cast.
ECC spokesman Grant Kippen said questionable results had so far been identified in Ghazni, Paktika and Kandahar provinces.
It is not yet known how many of the thousands of polling stations nationwide could be affected by the recounts and audits, he added.
A check by the BBC found 16 polling stations in Kandahar alone where more than 95% of votes had been cast for Mr Karzai.
More results are to be declared on Tuesday, but the BBC's Chris Morris in Kabul says many senior international officials believe they could be fraudulent.
In the latest results, published on Sunday, Hamid Karzai was within touching distance of the 50% threshold needed to avoid a run-off.
Nearest rival Abdullah Abdullah - who has claimed the vote amounted to "state-engineered fraud" - was about 17 percentage points behind.
But Afghan poll officials have also quarantined about 200,000 ballots.
Our correspondent says that if the Afghan administration is perceived to lack a legitimate mandate, fighting the Taliban, tackling corruption and spreading good government will become more difficult.
Election day was also marred by more than 400 Taliban attacks, including against voters whom the insurgents had warned not to turn out.
The fraud controversy comes as Washington considers whether to send thousands more troops to the country, where violence has hit a record high eight years on from the US-led invasion.
Mr Karzai told French newspaper Le Figaro on Monday that the US wanted him to be more docile, but "nobody has an interest in the Afghan president becoming an American puppet".