By Ranga Sirilal and Shihar Aneez
COLOMBO (Reuters) - A night of suspense lay ahead for Sri Lanka as voting ended in a presidential election that could hand Mahinda Rajapaksa a third term or bring to power a rival who has vowed to root out corruption and political decay.
Supporters of Mithripala Sirisena, a former government minister who deserted the president and changed sides to become the opposition's candidate in November, said figures showing a high voter turnout suggested a popular clamor for change.
"This means there is a strong sense that people need a change," said Rajiva Wijesinhe, one of more than two dozen lawmakers who defected from the ruling party in the run-up to Thursday's election on the Indian Ocean island.
But it was far from clear who would win and, adding to tension as election officials prepared to count millions of votes, police said hundreds of officers were on standby in the capital, Colombo, in case of trouble.
"We consider the next 6-7 days as the election period. Processions and protests are prohibited during this period," police spokesman Ajith Rohana told reporters.
"If anyone resists police action to secure law and order, we may have to use force."
Sri Lanka does not have a history of unrest over disputed elections. But a sitting president has never before been ousted and the prospect of this has fanned speculation the result could be distorted or even that the military might take control if Rajapaksa looks set to lose.
Rajapaksa won handsomely in the last election, surfing a wave of popularity that sprang from the 2009 defeat of ethnic Tamil separatists who had waged a crippling war against the state for 26 years.
Reminding voters of his triumph as polling booths opened, state-controlled television showed clips of Wednesday's attack in Paris by suspected Islamist militants and then switched seamlessly to old footage of the Sri Lankan war.
"When we see these images we also remember the history of terrorism in Sri Lanka," one announcer said.
Although his popularity has waned, Rajapaksa called the election two years early, confident that the perennially fractured opposition would fail to find a credible challenger.
He did not anticipate the emergence of Sirisena, who dined with the president one night and turned on him the next day.
Election officials said the turnout from an electorate of about 15 million was provisionally 65-80 percent. Results from districts will be announced through the night, but a clear winner may not emerge until early on Friday morning.
CORRUPTION AND AUTHORITARIAN STYLE
The Centre for Monitoring Election Violence, one of several observer groups, said there were two explosions in the Tamil-dominated north during the day and another at the house of a Muslim businessman in the south. No injuries were reported.
It said there were also several incidents of assault, threat and intimidation "allegedly by ruling party politicians and their supporters".
However, an international monitor from the Association of Asian Election Authorities said the vote was smooth and largely peaceful, even in the former war zone in the north.
The U.S. State Department said it was encouraged by reports of the high turnout and that election observers had been able to carry out their role. It also praised the election commission and security forces for ensuring a peaceful process.
Department spokeswoman Jan Psaki said the United States would wait for announcements from the commission and reports from domestic and international observer groups before making an assessment of the voting process.
"We urge the government of Sri Lanka to ensure that vote counting is carried out credibly and transparently and that any allegation of fraud or violence is credibly investigated," she told a regular news briefing.
Sri Lanka's economy has flourished since the war ended and many voters, especially ethnic Sinhalese Buddhists who represent 70 percent of the population, believe that sticking with Rajapaksa would keep living standards on an upward path.
But many complain of high living costs, rampant corruption and an authoritarian style that has concentrated power in the hands of the president's family.
On foreign policy, Rajapaksa has cold-shouldered neighboring India. He has also fallen out with Western countries, including the United States, that want an international investigation of suspected war crimes and criticize his record on human rights, turning instead to China as a strategic and investment partner.
Sirisena would lead a potentially fractious coalition of ethnic, religious, Marxist and center-right parties if he won. He has pledged to abolish the executive presidency that gave Rajapaksa unprecedented power and hold a fresh parliamentary election within 100 days.
He has also promised a crackdown on corruption, which would include investigations into big infrastructure projects such as a $1.5 billion deal with China Communications Construction Co Ltd to build a port city.
(Additional reporting by David Brunnstrom in Washington; Writing by John Chalmers; Editing by Andrew Roche and Meredith Mazzilli)