"President Tadic promised voters a European future for Serbia, " said state department spokesman Sean McCormack.
Mr Tadic wanted to gain EU candidacy to help him win re-election in spring.
Serbia can ill-afford to wait to see if that is going to be Tadic: the sequel.
ECONOMIST: Serbia��s presidential election: The gravedigger��s victory | The
The US has also congratulated Mr Tadic, saying it wanted to build a productive relationship with Serbia.
Mr Tadic described this as blackmail, and fought and won the election without his prime minister's support.
Still worse for Mr Tadic, most of the leaders of the Serbs in Kosovo's north are from opposition parties.
Serbia's president, Boris Tadic, wants a presidential election too, but this is being resisted by the prime minister, Vojislav Kostunica.
Serbia's electoral commission said Mr Tadic had secured 50.5% of the votes compared to Mr Nikolic's 47.7% in a closely monitored election.
Accompanied by Mr Tadic, Mr Erdogan visited Sandzak, Serbia's majority Bosniak south-western region, where the two men opened a Turkish cultural centre.
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May 26, 2011: Serbian President Boris Tadic announces the arrest of Mladic.
He fears that Mr Tadic's popularity might pull in votes for his Democratic Party, reducing Mr Kostunica's chances of becoming prime minister again.
Just two months after struggling to put together a European-leaning government in July, Mr Tadic now stands as the undisputed master of his country.
ECONOMIST: The Serbian president has become unusually powerful
Mr Tadic's party is more liberal, yet over the future of Kosovo, Serbia's secessionist southern province, Mr Tadic has been as hawkish as anyone.
Mr Tadic's Democratic Party (DS) and allies won 67 and the Socialist Party of Serbia (SPS) and partners, led by Ivica Dacic, won 44.
ECONOMIST: Serbia��s presidential election: The gravedigger��s victory | The
The ruling Democratic Party of President Boris Tadic hopes candidate status might boost its chances of winning the general election it may call early next year.
Mr Tadic's strategy of engaging the EU is evidently the better one for his people, even if it is a difficult one to promote at the moment.
Under the leadership of President Boris Tadic, Serbia has in recent years enjoyed a warming of relations with Brussels (the arrest of Mr Karadzic in July 2008 helped).
Ms Tadic and other activists are convinced that Western policy to work with the government rather than against it will fail, creating an organised crime hub in Montenegro.
This week Dusan Tadic, a Bosnian Serb who had treated Muslims in the camps brutishly, became the second person to receive a prison sentence from the Hague tribunal.
Serbia's government is bitterly divided between supporters of Mr Kostunica and backers of the president, Boris Tadic, who was conspicuous by his absence from the rally on Thursday.
The new government formed this month by President Boris Tadic has said that it wants to deal with the war crimes issue to remove any future obstacles to European integration.
Although ministers from Mr Tadic's party have been busy in Serbian parts of Kosovo in recent days, talking about developing them economically, Mr Tadic wants to halt Serbia's drift back into isolation.
What worries Milka Tadic, a well-known local journalist, is what would happen if President Vladimir Putin decided to gobble up Mr Deripaska's Rusal group, just as he did the oil giant Yukos.
The most likely option remains a coalition of the DS and SPS. But now that Mr Tadic is out of a job, some in his party want him to become prime minister.
ECONOMIST: Serbia��s presidential election: The gravedigger��s victory | The
Yet as kingmaker Mr Dacic dropped his alliance with the Democratic Party of Boris Tadic in favour of the Serbian Progressive Party (SNS) led by Tomislav Nikolic, who defeated Mr Tadic in the presidential election.
Serbia's president, Boris Tadic, has been trying to persuade the Serbian parliament to pass a resolution to condemn and commemorate the murder of up to 8, 000 Bosniaks by Bosnian Serb troops in Srebrenica in 1995.
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In a message to Mr Tadic, Jose Manuel Barroso, President of the European Commission - the EU's executive arm - said the result was "a victory for democracy in Serbia and for the European values we share".
Although Serbia's president, Boris Tadic, congratulated the Montenegrins on independence (and said he would be in charge of Serbia's armed forces), Mr Kostunica and the nationalists around him appeared barely capable of taking in what had happened.
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Vinci said it was significant that Karadzic's arrest had come just a few weeks after the appointment of a pro-western coalition government spearheaded by the Democratic Party of Serbian President Boris Tadic and new Prime Minister Mirko Cvetkovic following a narrow victory over nationalists in parliamentary elections in May.
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