Conakry - Guinea's main opposition leader Celloun Dalein Diallo withdrew on Wednesday from a presidential election, citing fraud, and he will not recognise the results, his campaign director said.
His decision came as the national election commission began to announce results from a vote held on Sunday that is expected to return incumbent Alpha Conde to a second five-year term in office in the West African country.
Guinea has a history of political violence linked to ethnic tension, including protests during the 2010 campaign that brought Conde to power. On Wednesday police fired tear gas at protesters in the capital and the government called for calm.
"However the results turn out, we will see that they have nothing to do with reality. In any case, we will not recognise them," said Diallo campaign director Aboubacar Sylla.
The Independent National Electoral Commission began to announce results late on Wednesday, though the process might not end until later this week.
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Early radio announcements had Conde with a sizeable lead. Most analysts, though, expected results to be close enough to require a second round, most likely against Diallo. It was not clear how his withdrawal would affect the process.
Millions of voters, around 75% of the population, cast their votes in Guinea's second free election in nearly 60 years since independence.
Conde spent years in opposition to military leaders and was imprisoned and exiled. His election in 2010 ended two years of military rule. One year earlier, security forces killed over 150 people in a stadium in Conakry and raped dozens of women.
Sunday's voting was calm and won praise from international observers, though one monitor urged caution in declaring the whole election fair before results have been announced.
Tension has been mounting amid allegations by Conde's challengers of fraud. Last Friday, at least two people were killed and 33 injured in fighting between supporters of Conde and his main rival Diallo.
On Wednesday, anti-riot police in the suburb of Koloma Soloprimo fired tear gas and warning shots as protesters began building street barriers, residents said.
"It is heating up over here. We are all hiding in our houses," said resident Souleymane Bah.
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A Reuters reporter on Monday saw three people with gunshot wounds at a local clinic after security forces and the opposition clashed overnight.
One of the injured, Bachir Barry, said he was hit in the hip as he was walking from the market.
"We are calling on everyone to give up on the street [protests]. If the institutions are not respected, then there is no rule of law," Foreign Minister François Lonseny Fall said at a meeting attended by press and foreign diplomats on Wednesday.
Justice Minister Cheick Sako said at the same meeting that those caught protesting would face criminal charges.
Dozens of anti-riot police vehicles circulated in opposition neighbourhoods, where burnt-out tyres and rocks littered the streets following the clashes late on Tuesday.