Sri Lanka's new government has ordered a criminal investigation into alleged corruption at the state-run national airline that it says involved "billions of dollars".

Prime Minister Ranil Wickremesinghe's office said an inquiry led by an anti-corruption lawyer had found "shocking details of corruption running into billions of dollars" at Sri Lankan Airlines, as well as "irregularities" in its $2.3 billion 2013 deal to buy 10 Airbus aircraft.

The statement, issued on Saturday, contained no allegations of wrongdoing by Airbus. The maker of planes said it had no comment on the Sri Lanka government statement.

According to the statement, the inquiry recommended investigations into the national carrier's "entire re-fleeting process".

The statement also said that former airline chairman Nishantha Wickremasinghe, who it identified as a brother-in-law of former president Mahinda Rajapaksa, "should be prosecuted".

Wickremasinghe rejected the findings of the inquiry on Monday. He said the airline was run by a board of competent directors and that all decisions were made transparently.

"The report is a character assassination. It is really frustrating. It was just an inquiry without giving any opportunity for me to explain my side of the story," he told Reuters. "They are crucifying me because of my relationship with the former president."

Wickremasinghe resigned as the airline's chairman shortly after Rajapaksa, who had been Sri Lankan president for 10 years, was defeated in a January election by Maithripala Sirisena.

The statement also said staff at the airline had knowingly ignored conflicts of interest with companies and individuals it hired, and that the inquiry found cases of the manipulation of contracts.

It also alleged that Rajapaksa changed the management of the loss-making airline, which is 51 percent government-owned, to ensure the purchase of the Airbus planes despite the availability of cheaper alternatives.

Rohan Weliwita, Rajapaksa's media coordinator, said on Sunday the former president had no comment yet on the government statement.

The corruption allegations are the latest in a series levelled at Rajapaksa by President Sirisena, who has ordered an investigation into all financial deals sealed by his predecessor.

Rajapaksa and former government officials have rejected the allegations and said they are ready to face any investigation.

Sri Lankan Airlines has a fleet of 21 aircraft including six Airbus A340 jets, seven A330s and eight A320 planes.

Under the deal with Airbus, the airline bought six A330s and four A350s, the European plane manufacturer said in a statement in 2013. Sri Lankan Airlines received the first of the A330s in October.

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