Along with Hasina, the now-former prime minster who fled to India after being toppled by a revolution in August, those subject to the inquiry include her son, Sajeeb Wazed Joy, and niece, Tulip Siddiq, a British lawmaker and government minister.

The allegations were raised by a writ seeking an investigation filed in the high court by Hasina's political opponent, Bobby Hajjaj, chairman of the Nationalist Democratic Movement party.

"We seek justice through our court", Hajjaj told AFP on Monday.

Key allegations are connected to the funding of the $12.65 billion Rooppur nuclear plant, the South Asian country's first, which is bankrolled by Moscow with a 90 percent loan.

A statement Monday from the commission said it had launched an inquiry into allegations that Hasina and family members had "embezzled $5 billion" from the Rooppur plant via "various offshore bank accounts in Malaysia".

It said its investigations were examining "questionable procurement practices related to the overpriced construction" of the plant.

"The claims of kickbacks, mismanagement, money laundering, and potential abuse of power raise significant concerns about the integrity of the project and the use of public funds", the commission said.

Graft allegations also include theft from a government building scheme for the homeless.

Hasina, 77, fled by helicopter on August 5 into exile in India, infuriating many Bangladeshis determined that she face trial for alleged "mass murder".

It was not possible to contact Hasina for comment.

Siddiq has "denied any involvement in the claims" accusing her of involvement in embezzlement, according to a statement from the British prime minister's office.

Joy, who is understood to be based in the United States, was also unavailable for comment.