The party of Malian presidential candidate Soumaila Cisse said on Monday that the poll would go to a run-off between Cisse and President Ibrahim Boubacar Keita, a day after a vote that was heavily disrupted by suspected Islamist gunmen.
Cisse's campaign manager, Tiebele Drame, made the announcement at the party's headquarters in Bamako, the capital.
Keita's spokesman said the president was substantially in the lead according to provisional vote count, although he accepted that a run-off was possible.
Spiraling jihadist violence has become a key issue in the campaign, as attacks multiply and the death toll mounts across north and central Mali.
"The law forbids the proclamation of results by anyone except the Ministry of Territorial Administration," Drame told a news conference. "However, I can tell you that we are going to a second round between Soumaila Cisse and Ibrahim Boubacar Keita."
Mahamadou Camara, the spokesman for Keita, said, "According to our tally, IBK has come substantially ahead," using the popular nickname for the president, taken from his initials.
The exact numbers of voters who were disenfranchised by violence is not known, but they could easily become a flashpoint if the vote is close. Ministry of Territorial Administration figures showed that, of the roughly 23,000 polling stations that were meant to open, 4,632 were disrupted by "armed attacks or other violence," of which 644 were unable to operate.
In most of Mali, the vote was peaceful and relatively well organized, with polls opening and closing on time. Most people who were enrolled and turned up were able to vote.
In the mud-walled medieval city of Timbuktu, once a flourishing tourist spot before Islamist militants made it too dangerous, witnesses said gunmen had intimidated voters, seized ballot boxes and in some cases set fire to them in the few polling stations that were attacked outside town.
"They came, they fired their weapons and then they took the ballot boxes away," witness and Timbuktu resident Insubdar Inaboud, 42, a bus conductor, told Reuters. Inaboud said he would have voted for Cisse, who hails from the region, if he had had the chance.
"I'm so angry. I don't think this vote is valid, because we are also Malians," he said.
Islamist militants took over northern cities like Timbuktu in 2012 on the back of a Tuareg rebellion, imposing Sharia law with harsh penalties like cutting off fingers for smoking, until France intervened a year later to push them back. The Islamist militants regard democracy as an un-Islamic Western imposition.
Since Keita came to power in the 2013 poll, Islamist violence has swept south into Mali's fertile center. U.N.
mission chief Mahamat Saleh Annadif on Friday urged whoever wins the poll to urgently address jihadist-stoked ethnic violence in Mali's central "breadbasket."
The figures from the ministry showed that the central region of Mopti accounted for half of polling stations under attack.
Hamid Bore, 39, a teacher, was in charge of one such station in the village of Dembere. The militants arrived just as polls opened at 8 a.m. (0800 GMT), he said.
"They were firing shots and then they asked for the bureau chief," he told Reuters by telephone. "They beat us up, then stole the ballot boxes and our bikes. I had to walk back. This is our only means of travel. How am I going to survive now?" At a news conference, the head of the European Union observer mission welcomed the decision to make public the number of polling stations that had not been able to function but urged it to publish more precise information about which ones exactly.
"The lists published by the government do not identify the polling stations precisely as we asked them to do," mission chief Cecile Kyenge said. "That makes...observing difficult."
A second round would temporarily cool tensions. Cisse's campaign has repeatedly accused Keita of tampering with the electoral list to try to steal the election.
"We contest in advance these contradictory results and demand a recount," Drame said.
The United Nations is heaping pressure on all sides to accept the result - or at least contest it through legal channels - to avert a political crisis on top of the security woes the country is already facing.