"Under cover of war victory, if someone is trying to boost up his family image or to stick to nepotism ... then you can't say peace has come."
President Rajapaksa's three siblings hold senior government positions.
The president's older brother is a cabinet minister, his younger brother an influential political adviser and his youngest brother is the country's defence secretary.
Separation of powers
Fonseka said if elected he would trim the powers of the country's executive and strengthen the parliament under a prime minister.
The presidency under the current system is so powerful that a serving president is immune to prosecution.
Government ministers and supporters have cited Fonseka's military background to argue that he, instead of giving up power, may become a dictator.
But Fonseka has said he has had ample opportunity in the past to do so if he had wanted.
The army under Fonseka has been widely criticised for its poor human rights record during the war earlier this year, which ended a 25-year fight for independence by the LTTE.
According to UN reports, more than 7,000 civilians were killed from January to May and a US state department report in October listed instances when government troops allegedly fired at civilians and hospitals and killed Tamil Tigers who surrendered under white flags.
Fonseka denied the army was involved in war crimes and implied gangs at the behest of political leaders may have been involved in attacks on journalists.
"As far as the army is concerned I don't know there were any war crimes. I monitored every action by the troops," he said.
"In my previous job I did justice to them [the Tamils]. I destroyed the terrorism and liberated the affected people," Fonseka said, adding that in his next job he would ensure "equal rights and justice done to all communities in the country".