Najib and former Treasury secretary-general Mohamad Irwan Serigar Abdullah were questioned by anti-graft investigators on Wednesday to help conclude the probe, the Malaysian Anti-Corruption Commission (MACC) said in a statement.

The two will be brought to a Kuala Lumpur court on Thursday to be charged, the MACC said.

"Both of them will be charged together in connection with an investigation into several cases of criminal breach of trust involving Malaysian government funds," it said.

The charges are linked to a multi-billion dollar scandal at 1Malaysia Development Berhad (1MDB), a state fund founded by Najib in 2009, a MACC source told Reuters.

Najib is already facing 32 money laundering, graft and breach of trust charges over more than 2.3 billion ringgit ($552.2 million) in transactions linked to 1MDB.

Read: Wife of Malaysia`s Former PM Najib Arrested by Anti-graft Agency

U.S. authorities allege that $4.5 billion was siphoned from the fund and that about $700 million was diverted into Najib's personal bank accounts.

Najib has pleaded not guilty and his trial is due to begin next year.

Separately, the MACC said similar charges would be brought against Malaysia's former foreign intelligence agency chief, Hasanah Abdul Hamid, on Thursday.

Hasanahand seven other agents of the Malaysian External Intelligence Organisation (MEIO) were detained in August in connection with the alleged misappropriation of government funds.

Authorities have frozen hundreds of bank accounts and blocked several people from leaving the country amid a wide-ranging probe into corruption launched by Prime Minister Mahathir Mohamad after Najib was ousted in a shock general election upset in May.

Najib's wife, Rosmah Mansor, and his former deputy, Ahmad Zahid Hamidi, have also been charged with corruption and money laundering. They have pleaded not guilty.

REUTERS