COLOMBO, Sri Lanka — Mahinda Rajapaksa, Sri Lanka’s president, was re-elected by a wide margin, election officials here said Wednesday, defeating the newly retired army general who had tried to lay claim to Mr. Rajapaksa’s biggest political victory, the defeat of the Tamil Tiger insurgency.

Official results gave Mr. Rajapaksa an 18-point advantage over his nearest opponent, Sarath Fonseka, the general who carried out the successful military operation against the Tigers. General Fonseka rejected the result, saying that the campaign had been marred by violence and irregularities in the vote counting. “The enthusiasm of the people we noticed in the campaign is not reflected in the result,” he said at a news conference.

Independent Sri Lankan election monitors said there was no evidence of major fraud in the voting, but left open the possibility of problems in the counting.

More broadly, election observers and advocacy groups have questioned the fundamental fairness of the campaign, accusing Mr. Rajapaksa of using state resources to run his campaign. State-owned news media all but shut out opposition candidates.

The election results illustrate the still yawning ethnic and religious divides that plunged Sri Lanka into civil war in the first place, and underscore the difficulties that Mr. Rajapaksa will face in trying to reconcile the country after 26 years of conflict.

General Fonseka spent the day secluded in a five-star hotel, which the government surrounded with commandos, saying they had been placed there for security reasons. He said he feared for his safety. “They are trying to make me a prisoner,” General Fonseka said, addressing a conference room packed with journalists. “They have made things very clear today.”

Lucien Rajakarunanyake, a government spokesman, rejected the suggestion that General Fonseka was in danger, saying that the troops outside the hotel were merely for his safety. “He is free to leave at any time,” the spokesman said.

The Tamil Tiger insurgency fought to create a Tamil homeland in the north and east of Sri Lanka, separate from the Sinhalese majority. But over the years the group became little more than a criminal enterprise famous for its cruel tactics, human rights groups say, like holding civilians as human shields as well as using child soldiers and female suicide bombers.

While Mr. Rajapaksa won a big majority, Tamil and Muslim voters largely rejected him. Mr. Rajapaksa pledged to be a president for all Sri Lankans, not just those who voted for him, an apparent effort to reach out to Tamil voters who shunned him in large numbers.

“Six million people voted for me,” Mr. Rajapaksa said at a news conference on Wednesday evening. “Even the people who voted for other candidates, I have to look after their interests.”

It had been an ugly and sometimes violent campaign between two men who had once been close allies. The evidently exasperated elections commissioner, Dayananda Dissanayake, described numerous transgressions by the government during the campaign, concluding that “state institutions operated in a manner not befitting state organizations.” Guidelines for the state media to behave fairly toward both candidates were ignored, he said, adding that the stress of overseeing the election had taken a toll on his health.

A long night of counting ballots confirmed that turnout in northern Tamil areas was very low, in the single digits in some war-hit areas, while voters had flocked to the polls in Mr. Rajapaksa’s southern stronghold.

Dayan Jayatilleka, a political analyst who was Sri Lanka’s representative to the United Nations in Geneva until the government fired him last year, said that the Tamil political parties had lost touch with the electorate during the war. “They have been engaging in the politics of exile,” Mr. Jayatilleka said. “They have not done the hard yards of rebuilding their political network.”

But election observers said that explosions and other disturbances, along with the heavy militarization of the northern and eastern Tamil areas, had also suppressed the vote.

The other political parties in General Fonseka’s coalition also struggled to bring in voters. The center-right United National Party failed to deliver the capital, Colombo — its stronghold — for General Fonseka. And the Marxist party known as the J.V.P., the Sinhalese acronym for People’s Freedom Party, seemed to make little headway against the president in its southern Sinhalese bastions.

General Fonseka, who ran on his record of winning the war against the Tamil Tigers, had counted on support from Tamil voters, who he hoped would choose him over Mr. Rajapaksa as the more palatable of the two options. Though General Fonseka led the military campaign that may have killed thousands of Tamil civilians, he portrayed himself as committed to healing ethnic divisions and allowing communities a greater measure of self-rule.

He also sought to capitalize on dissatisfaction with Mr. Rajapaksa in some quarters of the Sinhalese majority. Voters expressed concern about the concentration of state power within Mr. Rajapaksa’s family. One of his brothers is the powerful secretary of defense, another is a senior adviser, and many members of his extended family work in senior government positions.

But Mr. Rajapaksa emerges from the election in many ways stronger than ever. He ran on his war record, arguing that if he delivered on his pledge to win the war he could also bring a peace dividend and heal the nation’s ethnic rifts.

“The president keeps his promises,” said Gamage Banduwathie, a voter who left the United National Party to support Mr. Rajapaksa. “I hope that he will be a savior for Sri Lanka.” IHT