A Sri Lankan high court has sentenced the former army chief, Sarath Fonseka, to three years in jail after finding him guilty of making a false allegation against the president's brother.
Fonseka, who ran against President Mahinda Rajapaksa in the 2010 elections, is already serving a 30-month prison term after a court martial convicted him of irregularities in military procurements.
Fonseka was found guilty on Friday of spreading rumours that Gotabhaya Rajapaksa, the president's brother and Sri Lanka's defence secretary, had ordered the killing of Tamil Tiger leaders as they tried to surrender in May, 2009.
Al Jazeera's Minelle Fernandez reporting from Colombo said: "Fonseka was seen as a hero" after leading his country to victory over the Tamil Tigers in 2009.
Fonseka subsequently fell out with the government and says the legal cases against him are politically motivated.
He faces yet another case in which he is accused of harbouring military deserters who he allegedly used as bodyguards during his failed election challenge against Rajapaksa.
He was arrested shortly after the 2010 presidential poll.
He was charged with "spreading disaffection" after he gave a newspaper interview apparently giving credence to allegations that Gotabhaya Rajapaksa ordered war crimes.
Fonseka says he was quoted out of context in the Sunday Leader article published on December 13, 2009.