A polling station chief was killed by suspected jihadists in northern Mali as insecurity disrupted a presidential runoff on Sunday.
Security had been drastically boosted ahead of the election's second round between President Ibrahim Boubacar Keita and former finance minister Soumaila Cisse. But several polling stations were closed in the restive central and northern regions due to security concerns.
"Jihadists came this Sunday around 13:30 to a polling station in Arkodia," in the restive northern Timbuktu region, a local official told AFP.
"They asked everyone to put their hands up. The polling station president tried to escape. The jihadists shot and killed him," the source said.
The first round vote on July 29 was marred with violence and threats from armed groups that led to several hundred polling stations being closed - but no casualties had been reported.
Authorities in the vast West African nation said Saturday they had disrupted a plot to carry out "targeted attacks" in the capital Bamako on the eve of the vote.
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Sunday's ballot in Mali is a rerun of a 2013 faceoff between Keita, 73, and Cisse, 68, amid a wave of jihadist bloodshed and ethnic violence.
This year's campaign saw fierce attacks on Keita's perceived failure to halt the violence, as well as mounting accusations of vote fraud.
But public enthusiasm has been low and the opposition is fractured.
"We hope the new president does better and knows how to make up for past mistakes," El Hajd Aliou Sow, a retired civil servant, told AFP as he left a group of early-morning voters.
Mali, a landlocked nation home to at least 20 ethnic groups where the majority of people live on less than $2 a day, has battled jihadist attacks and intercommunal violence for years.
After the first-round vote the pool of candidates was reduced from 24 to two, as Keita was credited with 42% of the vote and Cisse picked up 18 percent.
Keita cast his vote in Bamako shortly after 0900 GMT Sunday and warned against "staged" electoral fraud after accusations of ballot box stuffing and other irregularities.
"How could you stage fraud when you are assured of the support of your people?" Keita said.
Cisse's party told AFP in the early hours of Sunday that ballot papers were already circulating, several hours before polls opened.
The three main opposition candidates had mounted a last-ditch legal challenge to the first-round result, alleging ballot-box stuffing and other irregularities. But their petition was rejected by the Constitutional Court.
Cisse has failed to unite the opposition behind him, and first-round challengers have either backed the president or refused to give voting instructions.
Local observers said voter turnout was low by the afternoon, the West Africa Network for Peacebuilding (WANEP) said in a statement.
Polling stations closed
Voting will close at 18:00 GMT and results are expected within five days. Turnout was low in the first round at around 40%.
Security had been tightened for the second round, an aide in the prime minister's office said, with 20% more soldiers on duty.
But voting could not take place in several areas, including the northern village of Kiname, 120km from Timbuktu, where "armed men came and took all the voting material to the river bank and set it on fire", a resident told AFP.
"There was no voting in Toguerekotia in the Sossobe district (of the central Mopti region) because of insecurity," WANEP, which has 150 observers across the country, said in a statement.
Outside Mali, the hope is that the winner of the election will strengthen a 2015 accord that the fragile Sahel state sees as its foundation for peace.
The deal brought together the government, government-allied groups and former Tuareg rebels.
But a state of emergency heads into its fourth year in November.
Jihadist violence has spread from the north to the centre and south of the vast country and spilled into neighbouring Burkina Faso and Niger, often inflaming communal conflicts.
France still has 4 500 troops deployed alongside the UN's 15 000 peacekeepers and a regional G5 Sahel force, aimed at rooting out jihadists and restoring the authority of the state.