Former army commander and war hero Sarath Fonseka has begun a three-year sentence in a Colombo jail for implicating the government in alleged war crimes.

The ruling ends what became known as the "White Flag" case, a 16-month trial against Fonseka, who led the mostly Sinhalese ethnic majority army to victory against the rebel Tamil Tigers in 2009.

A three-judge court ruled Fonseka had lent credence to allegations the defense secretary ordered Tamil Tigers to be killed as they tried to surrender in May 2009.

Fonseka, 60, was found guilty of inciting violence in an interview given to the English weekly newspaper Sunday Leader.

In the article, in which the court said he was "spreading disaffection," Fonseka allegedly backed accusations that Defense Secretary Gotabhaya Rajapaksa had ordered the army to shoot Tamil Tiger cadres surrendering with white flags during the final stages of the war. Gotabhaya is the brother of President Mahinda Rajapaksa.

On this charge, one of the three judges dissented from the guilty verdict of the other two judges.

The celebrated army chief, who denies all the allegations, was already serving 30 months after a court-martial convicted him of irregularities in army procurement.

But Fonseka likely will return to a courtroom to face other charges of harboring army deserters.

The verdict is the latest chapter in a spectacular downfall of the decorated former general from national savior to jailed criminal.

Fonseka unsuccessfully contested the presidential election in January 2010 as the candidate for the New Democratic Front party.

But a court-martial in August last year sentenced him to 30 months in jail and gave him a dishonorable discharge for engaging in politics while being in active service, the ColomboPage news Web site reported. The retired military chief was stripped of his ranks and medals he earned during his 40-year carrier.

Fonseka is a staunch nationalist of the Sinhalese ethnic majority that was fighting a decades-long civil war against Tamil separatists. His downfall began when he fell out with his ideological soul mate, President Rajapaksa, shortly after the war over who should claim credit for the victory, the BBC reported.

Political reverberations continue from the protracted civil war in which the United Nations estimates around 100,000 people were killed, including up to 7,000 in the final, particularly brutal, year of fighting. Tamil Tiger rebels were struggling for a separate homeland for Tamils in the northeast of the island nation that lies only several miles off the southern tip of part of the Indian subcontinent.

The government continually denies allegations of suspected war crimes and slammed what it said was a biased U.N. report published in April. The government said it feared the U.N. report, based on 10 months of work, could rekindle nationalistic flames and destroy trust on both sides.

"Among other deficiencies, the report is based on patently biased material which is presented without any verification," the Sri Lankan External Affairs Ministry said in a statement.

Rajapaksa called for people to demonstrate in the streets on the traditional May Day celebrations in what he said would be a "show of strength" against the report.

"The time has come to show our strength and this should not be confined to expressing worker solidarity on this day but also to demonstrate against the injustice done to the country before the world," Rajapaksa said.

"I am prepared to face any punishment on behalf of the motherland with great honor."