Incumbent Mahinda Rajapakse took a strong lead in counting Wednesday from Sri Lanka's bitterly disputed presidential election, officials said, as armed troops surrounded the hotel of his main rival.
Election officials said Rajapakse, who is being challenged by his estranged former army chief Sarath Fonseka, had won 60 percent of the vote with about a fifth of the ballots counted.
The winner of the island's first election since last year's defeat of a three-decade insurgency by ethnic Tamil rebels was set to be announced around midday (0630 GMT).
Tensions were acute in the capital Colombo, where up to 80 armed soldiers ringed the de-luxe hotel where Fonseka was staying with several other opposition leaders.
"We have surrounded the hotel," a military spokesman told AFP. "We have information that there are 400 people including army deserters inside. We have sent word for them to surrender," he said.
An opposition spokesman complained that the military presence was intended to "intimidate us or arrest our leaders".
State television had earlier warned that Fonseka was "hatching a conspiracy against the victory of the president".
The campaign's vitriolic nature, the personal animosity between the two main candidates and tit-for-tat accusation of coup plots have all fuelled concerns that any result would be contested and foment new unrest.
Tuesday's election was the first since Rajapakse, 64, and Fonseka, 59, engineered the final defeat of the Liberation Tigers of Tamil Eelam (LTTE) who had been fighting for a Tamil homeland in the island's northeast since the 1970s.
Partial official results showed Rajapakse with 1.31 million votes against 862,644 for Fonseka. An estimated 9.85 million people voted in all.
Media Minister Anura Priyadharshana Yapa said Rajapakse, who like Fonseka is a member of Sri Lanka's dominant Sinhalese community, was "heading for a historic victory".
"Personally, the outcome is better than what I expected," Yapa said.
In a further twist, the government said it would challenge the legitimacy of Fonseka's candidacy in court after it emerged that he was unable to cast a ballot on Tuesday because his name did not figure on the electoral roll.
The government argued that Fonseka was therefore ineligible for the presidency, despite a strong statement to the contrary from the independent election commissioner.
"What the election commissioner has expressed is merely an opinion, but the courts have the ultimate authority to interpret the law," Foreign Minister Rohitha Bogollagama told reporters late Tuesday.
Four people were killed and more than 1,000 election-related incidents were reported to police in the run-up to Tuesday's contest.
Opposition leader Ranil Wickremesinghe, whose disparate forces backed Fonseka on an anti-corruption platform against the president's alleged family nepotism, said the election had been "by and large" peaceful.
There were a number of violent incidents during voting, including bomb attacks in the northern Tamil stronghold of Jaffna, which monitors said had deterred some people from voting.
Rajapakse as commander-in-chief and Fonseka, his army chief, defeated the Tamil Tigers in May last year, ending a separatist conflict that left 80,000-100,000 dead, according to UN figures.
The military campaign made both men national heroes in the eyes of the Sinhalese-majority electorate but has since been mired in allegations of war crimes. Some 300,000 Tamils were herded into internment camps.
Rajapakse has ruled Sri Lanka since 2005. His three brothers and other family members are in key government positions including the ministries of defence and ports.