Insecurity is such that in some parts of the country the vote will simply not happen

* President Ibrahim Boubacar Keita seeking a second mandate

* Insecurity has worsened and spread since he took power

* Dispute over electoral list raises fears of poll violence (Adds quotes)

By Tim Cocks and Tiemoko Diallo

BAMAKO, July 29 (Reuters) - Malians began voting on Sunday to decide whether or not to give President Ibrahim Boubacar Keita a second term, amid widespread ethnic and jihadist violence that has dramatically worsened since he came to power five years ago.

Two dozen other candidates were contesting the presidency in a largely Saharan desert nation that has been fractured by a Tuareg rebellion and Islamist militancy across its north and central zones since the last poll in 2013.

Insecurity is such that in some parts of the country the vote will simply not happen, and the European Union observer mission urged the government on Saturday to publish a list of places that will be unable to vote, so as to quell suspicions by candidates of "fictitious polling stations."

"These are polling stations in which we know insecurity ... won't make the vote possible there," EU mission head Cecile Kyenge told journalists on Saturday.

Eight million voters are enrolled. Voting began as scheduled at polling stations in the capital Bamako at 8 a.m. (0800 GMT). Polls close at 6 p.m. Opposition candidates include businessmen, an astrophysicist, and just one woman.

The threat of violence was on the minds of voters as they voted on Sunday morning, a fact which could reduce turnout in a country where normally only 40 percent vote on average.

"I was scared to come and vote because of the insecurity, but I feel relieved because everything went well," said 26-year-old housekeeper Mariam Cisse who voted in the fabled northern medieval Islamic city of Timbuktu, once a popular tourist spot until it became beset by Islamist militancy in 2012.

"I voted for Soumaila Cisse because I wanted power to change hands," she said, referring to the 68-year-old candidate considered the most likely to beat the incumbent president.

A Reuters witness said it was calm in Timbuktu on Sunday after days of unrest leading up to the polls.

One thousand km (600 miles) southwest in the capital Bamako, 32-year-old Hama Diallo just hoped for a safer future. "I am fulfilling my duty as a citizen. I hope the President-elect makes security a priority, without which nothing is possible".

In the past three years, jihadist attacks have tripled and violent deaths doubled, according to civil society website Malilink. Islamists have spread from the north to the centre and even targeted Bamako - as in 2015, when gunmen killed 20 people in a raid on a hotel - as well as Mali's neighbours.

Last month a suicide bomber drove a vehicle laden with explosives into the headquarters of the regional G5 Sahel anti-terrorist force in Severe, central Mali, killing three people.

"POSSIBLE DISPUTE"

Growth has averaged five percent under Keita, and Mali's key exports of gold and cotton have flourished, as have agricultural staples like rice, but insecurity has taken the shine off.

The United Nations peacekeeping mission to Mali has suffered more deaths than any in history, with some 170 peacekeepers killed, and human rights groups have raised the alarm over alleged executions by security forces. The Defence Ministry promised to investigate evidence linking them to mass graves.

Malian elections meanwhile have always been peaceful. Yet opposition candidates have cried foul over alleged tampering of the electoral list, and Cisse told supporters on Friday the government was planning to steal the election.

"We have discovered ... massive fraud. This is a government that cheats," said Cisse, who is from a village near Timbuktu.

Keita rejected this as "false" as he voted on Sunday in his home constituency of Sebinikro outside Bamako, a neighbourhood of dirt roads where chickens peck at piles of trash.

"There has only ever been one electoral roll in Mali," he told journalists, wearing trademark white kaftan and skull cap.

Western countries such as France, as well as the United Nations, are heaping pressure on all sides not to allow any dispute to boil over into violence.

On Saturday a spokesman for U.N. Secretary General Antonio Guterres urged "all political actors in Mali to commit to making this poll a peaceful, free and transparent process."

(Additional reporting by Marina Depetris in Bamako and Maita Moro in Timbuktu Editing by Edward McAllister, William Maclean)

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