Mali's President Ibrahim Boubacar Keita will face opposition figure Soumaila Cisse in a run-off vote on August 12 after neither secured more than 50% in the first round of the presidential election, an official said late on Thursday.In Sunday's poll Keita won 41.42%, with Cisse polling 17.80%, according to provisional results, said Territorial Administration Minister Mohamed Ag Erlafk on ORTM public television.Businessman Aliou Diallo came third with 7.95% and former transitional prime minister Cheick Modibo Diarra, an astrophysicist who held that office for eight months in 2012, completed the top four with 7.46%.* Sign up to News24's top Africa news in your inbox: SUBSCRIBE TO THE HELLO AFRICA NEWSLETTERFOLLOW News24 Africa on Twitter and Facebook.Voters in the vast west African country had 24 candidates to choose from in the key poll for the troubled Sahel region."Thanks to you, I'm in the lead," Keita, 73, who is seeking a second five-year term, said on his campaign Twitter account. "This is clear evidence of your trust."The second round on August 12 will be a repeat of the 2013 run-off, with Keita again facing former finance minister Cisse."I was expecting a single round, the voters decided otherwise," said Mamadou Wague, an activist with the ruling party, predicting Keita would finally win a victory "even more emblematic than 2013," when he took more than 77% of the vote.Linchpin Sahel stateAhead of the announcement, challengers Cisse and Diallo had said they would not accept the election results "marred by irregularities"."For the first time in the history of Malian democracy, a president in office is forced to a second round," Cisse, 68, said on Twitter after the results, adding that the plan to have Keita re-elected in the first round had failed "despite the fraud".Turnout was 43.06%, rather higher than the average seen in Mali where less than a third of over-15s are literate.The international community hopes the poll will strengthen a 2015 accord that Mali, a linchpin state in the Sahel region, sees as the cornerstone for peace.On the campaign trail, Keita - commonly known by his initials IBK - had highlighted the achievements of the peace agreement between the government, government-allied groups and Tuareg former rebels to fight jihadist fighters in the country's north.Cisse, and other challengers, however have accused Keita of incompetence on security matters.Attacks disrupted voting on Sunday in areas already beset by deadly ethnic and jihadist violenceAround 700 of the 23 000 polling stations - mainly in the north and centre of the country - were unable to open due to violent incidents, but the polling "went ahead calmly" throughout the rest of the country, EU monitors said.Violence also marred the lead-up to the vote, despite the presence of 15 000 UN peacekeepers and 4 500 French troops and a much-heralded five-nation anti-terror G5 Sahel force. A state of emergency will enter its fourth year in November.Jihadist violence has spread from northern Mali to the centre and south of the country and spilt over into neighbouring Burkina Faso and Niger, often inflaming communal conflicts.Mali is one of the world's poorest countries, with most people living on less than $2 a day.