Sri Lanka's new government has asked police to investigate what it called a "diabolical conspiracy" by former president Mahinda Rajapaksa to hold on to power after being defeated in an election last week.

Rajapaksa has denied the allegations against him. His allies say they have been subjected to threats since the election and they have asked for government protection.

Foreign Minister Mangala Samaraweera, who filed the latest police complaint, said the government had reliable information that Rajapaksa along with his brother and former defence secretary Gotabaya Rajapaksa, the incumbent chief justice and two other politicians discussed declaring a state of emergency while the counting was going on.

The former president and his associates have come under a level of scrutiny which was unthinkable until Rajapaksa was voted out of office last Thursday, ending a decade in power notable for its concentration of control among a coterie of relatives and allies.

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Newly-elected President Maithripala Sirisena is trying to shore up his government and prevent a comeback by the former rulers in parliamentary elections that may have to be held this year.

The AFP news agency reported on Thursday that Rajapaksa had agreed to step down as head of the Sri Lanka Freedom Party, allowing Sirisena, who defected in November to fight the election, to claim the party leadership.

On Wednesday, he replaced ex-military general GA Chandrasiri with civilian HMGS Palihakkara as the new governor in the Tamil-controlled north, in a sign of improving ties with the ethnic minority following the end of the civil war.

Opposition politicians have filed a series of detailed corruption complaints against Rajapaksa and his brothers and son, who also held government posts. Another filing asks for Rajapaksa to appear in court on January 26.

Rajapaksa's family also stands accused of amassing huge wealth during his 10-year rule. Police say they are investigating the disappearance of a fleet of luxury presidential cars as he vacated his official residence.

Source: Al Jazeera and agencies