Updated

Serbia, a landlocked nation of 7.1 million in southeastern Europe, is holding a presidential runoff vote on Sunday. The outcome holds the key to Serbia's bid to join the European Union as well as its relations with Kosovo, a former province whose declaration of independence Serbia has refused to accept. The nationalist opposition has accused pro-EU reformists of rigging the May 6 general vote, including the first-round presidential ballot, which has raised tensions ahead of the runoff on May 20.

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PRESIDENTIAL RACE: The president is elected to a five-year term. Whoever holds the position commands the army, names the prime minister and signs laws passed by Parliament. Boris Tadic, the pro-EU former president, is seeking a third term. He is being challenged by Tomislav Nikolic, who has Russia's backing.

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TADIC: The leader of the pro-Western Democratic Party has championed Serbia's bid to join the European Union. Under his leadership, the country became a candidate for entry in March. The 57-year-old psychology professor says his re-election would bring stability to crisis-stricken Serbia. Tadic's camp is promising foreign investment and better ties with Serbia's neighbors. Tadic has rejected independence of Kosovo, but he has opened talks with the former province and is seen as taking a more conciliatory stance. He has promised a fight against widespread corruption in Serbia. He is married with two children.

NIKOLIC: The leader of the populist Serbian Progressive Party is a former extreme nationalist who has recently embraced a more moderate position. Nikolic was the deputy leader of the extreme-right Serbian Radical Party until three years ago, when he split and formed his own party. He has moved from a staunchly anti-Western stance to a pro-EU one, a change liberal Serbs view with suspicion. The 60-year-old former cemetery manager has lost twice against Tadic in seeking the presidency. He has garnered support in Serbia by promising to root out alleged crime and corruption during the transition to a market economy. He is married with two children.

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FACTS: About 8,500 polling stations open at 7 a.m. (0600 GMT) and close at 8 p.m. (1900 GMT) on Sunday. Unofficial results expected within an hour or two after polls close, with a complete official count likely Monday or Tuesday.