The results of the first round of Mali's presidential election will be announced on Friday, a day later than expected, the presidency said Thursday.

No explanation was given for the delay, announced by the presidency's Twitter account, but an official from the ministry of territorial administration said vote-counting had not been completed following Sunday's poll.

Initial results showed on Tuesday that former prime minister Ibrahim Boubacar Keita had taken a wide lead, and interior minister Moussa Sinko Coulibaly said there would be no need for a second round vote on August 11 if the trend continued.

But the party of Keita's rival Soumaila Cisse said Wednesday the election had been marred by "ballot stuffing," a form of electoral fraud in which people submit multiple ballots during a vote in which only one ballot per person is allowed.

The Union for the Republic and Democracy (URD) has accused Coulibaly's department of having "failed in its duties" and called for him to be sacked.

Although there were 27 presidential hopefuls, analysts have characterised the election as a two-horse race. Keita was seen as the frontrunner ahead of Cisse, a former finance minister and erstwhile chairman of the Commission of the West African Economic and Monetary Union.

Sunday's vote was the first since an uprising by Tuareg separatists sparked a military coup in March last year which toppled democratically elected president Amadou Toumani Toure, plunging Mali into a political crisis and opening the way for Islamists to occupy the vast desert north for 10 months, before being ousted by a French-led military offensive.