COLOMBO (AFP) - Sri Lanka's Marxist opposition party has filed a corruption complaint against former president Mahinda Rajapaksa and his family and asked the anti-graft body to prevent them leaving the country, a spokesman said Wednesday.

The JVP, or People's Liberation Front, has lodged the complaint against Mr Rajapaksa, his legislator son Namal and two brothers - Basil and Gotabhaya - who held powerful positions in the former president's administration that was ousted after last week's elections.

The election was partly fought on claims of misuse of public funds and nepotism, with the Mr Rajapaksa family accused of massing huge wealth during the ex-president's 10-year rule.

"The main objective of our complaint is to ensure that the Mr Rajapaksa family is brought to justice," JVP lawmaker Sunil Handunetti said. "We want to prevent them from fleeing the country and escaping justice."

He said a total of 12 individuals have been named in the complaint as alleged offenders including former finance secretary Punchi Banda Jayasundera and ex-central bank governor Nivard Cabraal. They have been accused of foreign exchange fraud, land grabs and misusing state property.

The anti-corruption unit has been ineffective since its inception due to political interference, but new President Maithripala Sirisena has pledged to introduce laws making it more independent and giving it more power to prosecute offenders.

Mr Rajapaksa on Tuesday said he would not flee the country and denied allegations he attempted a coup to retain power after it became clear that he had lost the election.

The new government has vowed to investigate claims made by Mr Sirisena's top aides that Mr Rajapaksa tried to mobilise the military to keep him in office.

The new government is also investigating the disappearance of a fleet of luxury cars that went missing from the president's office as Mr Rajapaksa vacated his official residence.

His family has been accused of massing wealth as they controlled nearly two thirds of the country's national budget.

During the election campaign, allegations emerged that the Mr Rajapaksa family had padded the price of a new highway to US$16 million (S$21 million) per kilometre - allegedly more than double the actual cost.

The family was also accused of inflating the cost of a new Chinese-built railway to more than 12 times the actual price at US$18 million per kilometre. An Indian company built an equivalent track for US$1.5 million per kilometre.