UPDATE 3-Guinea decides on third term for Conde amid voter-card concerns
(Adds background and quotes from opposition leader and voters)
* Conde, 82, secured constitution change to run again
* Analysts expect him to defeat long-time rival Diallo
* New constitution triggered violence over past year
* Voters nervous, problems reported with voter cards
CONAKRY, Oct 18 (Reuters) - Voters in Guinea went to the polls on Sunday to decide whether to extend the rule of 82-year-old president Alpha Conde, who in March pushed through constitutional changes allowing him to run for a third term.
At least 50 people have been killed over the past year during demonstrations against the new constitution, according to Amnesty International, and violence erupted repeatedly during campaigning.
There were no reports of unrest on Sunday, but a number of people including one of the candidates said they had been turned away at polling stations because of problems with their voter cards.
The election comes at a delicate moment in West Africa, where concerns are growing over a slide in democratic gains. In August, Mali's government was overthrown by the army, while in Ivory Coast, months of protests against President Alassane Ouattara's bid for a third term on Oct. 31 have turned violent.
In the west of Guinea's capital, Conakry, dozens of voters queued quietly to vote in a primary school whose exterior was plastered with posters of Conde.
"I hope that things will happen in peace," said Mariama Camara, a housewife.
But across town in the Koloma Soloprimo neighborhood, an opposition stronghold, several voters told Reuters they had been unable to participate because of voter card problems.
"When I arrived at the polling station, I was told my card was not valid," said resident Fatoumata Barry.
While no reliable opinion polls are available, many political analysts expect Conde to prevail after he won overwhelming approval for the new constitution in a referendum in March - although that vote was boycotted by the opposition.
"A HOLY MESS"
Conde faces 11 challengers, including his long-time rival Cellou Dalein Diallo, a former prime minister who finished runner-up to Conde in elections in 2010 and 2015.
After casting his vote, Diallo said he was worried that Conde would steal the election with "cunning and violence."
"We will not accept (that)," he said.
One of the candidates, former foreign minister Makale Camara, said she herself had not received a voter card at all, and so had been unable to vote.
"That's totally unacceptable because there are people who ended up with three or four cards," she told Reuters.
"It's a holy mess they've organized there. If there can be 'fictitious' citizens, a candidate cannot be fictitious."
Conde, who has described the constitutional reform that allowed him to run again as fair and democratic, says he needs more time to finish major mining and infrastructure projects in the West African country.
"Guinea cannot develop if there is no peace, security and unity. We do not want violence," he said after casting his ballot at the Boulbinet primary school in Conakry.
"Those who want to challenge the results must do so within a legal framework, with recourse to the Constitutional Court," he added, dressed in white and flanked by bodyguards.
Guinea has made progress developing its mineral riches, including bauxite and iron ore, and gross domestic product has doubled under Conde's presidency. But many Guineans complain the mining boom has not ended frequent power cuts and unemployment.
In response to Reuters' question about potential voting irregularities, election commission spokesman Mamadi 3 Kaba said: "Only cards distributed over the last 30 days are valid."
(Writing by Hereward Holland; Editing by Kevin Liffey)
© Copyright Reuters Ltd. All rights reserved. The information contained in this news report may not be published, broadcast or otherwise distributed without the prior written authority of Reuters Ltd.