MACC has summoned Najib Abdul Razak and former Treasury secretary-general Irwan Serigar Abdullah for questioning at the commission's headquarters in Putrajaya tomorrow, according to sources close to the 1MDB investigations.

The sources told Malaysiakini that the former premier and Irwan were called to facilitate probes into the state investment arm's dealings with Abu Dhabi wealth fund, International Petroleum Investment Company (IPIC).

"They (Najib and Irwan) have been called to appear at the MACC headquarters at 2pm tomorrow over IPIC," said one of the sources.

This would be the third time MACC has summoned Najib for questioning over 1MDB's dealings with IPIC this month.

In previous cases involving SRC International and 1MDB, MACC had detained Najib overnight before charging him in court the next day.

Earlier today, a source close to the investigation confirmed with Malaysiakini that Najib would face an additional six charges on Thursday, bringing the total of charges against him to 38.

Malaysiakini learnt that investigations into the 1MDB/IPIC affair had made progress following information obtained from a person involved in the matter.

The source told Malaysiakini that the person, who carries a "Datuk" title, was appointed by Najib as an intermediary for the two companies some years ago.

New Straits Times had earlier reported that Najib was expected to face at least four more charges this week related to 1MDB's dealings with IPIC.

It said that prosecutors would hold Najib liable for his role in last year’s debt settlement between the two parties.

'Go after IPIC'

Sources had told the NST that MACC investigators had looked into how the former administration had settled a debt using taxpayers' money and who had authorised the payment allegedly “without the approval of the cabinet”.

A settlement was reached last year by the Finance Ministry to pay US$1.2 billion (RM5.04 billion) to IPIC over a US$6.5 billion claim made by the latter. Najib was also the finance minister then.

Najib had in Parliament earlier today told Putrajaya to go after IPIC over the US$3.5 billion in missing Malaysian funds, this as he himself is to be charged over his administration's dealings with the Abu Dhabi firm.

The former premier said in the Dewan Rakyat that his government inked an agreement with IPIC in 2015 through which Malaysia would receive US$1 billion from the firm while IPIC also "agreed to return US$3.5 billion."