The Special Investigating Unit (SIU) wants to conclude its investigation into Health Minister Zweli Mkhize and Digital Vibes by June, the corruption-busting agency's head Andy Mothibi told the Standing Committee on Public Accounts on Wednesday.

Mothibi confirmed that Mkhize's role in the alleged corrupt tender is being investigated.

In February, Daily Maverick broke the story that Digital Vibes, a then-obscure communications company whose consultants - Mkhize's former personal spokesperson and family friend Tahera Mather and his former private secretary Naadhira Mitha - secured an irregular communications contract from the Department of Health.

The contract was worth R82-million for work related to the Covid-19 pandemic.

Last week, Daily Maverick revealed that the department paid more than R150-million to Digital Vibes, which also included payments for services not related to Covid-19, and that Mkhize, contrary to his public denial, had benefitted personally from the contract.

President Cyril Ramaphosa has said publicly that he would only act on the matter after the SIU finalised its investigation.

Last week, Mothibi said the SIU investigation was ongoing and at an advanced stage.

"Our investigators have been going through the procurement process in the department," he said.

"To date, we can report that – and this the department announced themselves – the procurement process has been irregular."

He said they were still investigating other aspects of the contract.

"We have determined the accountability levels of who was actually involved in the procurement process, and referrals will be made to the department.

"We will also be looking at various allegations made at officials at the department, including the executive authority at the department and the service provider that has been identified, Digital Vibes," Mothibi said.

The executive authority is the minister - Mkhize.

Mothibi said at this stage he is "really constrained" to divulge further details as it could prejudice the investigation.

"We are investigating all those allegations, and the investigation is progressing well."

He said Mkhize has "expressed his cooperation".

The investigating team was still following legal prescripts and would interview witnesses under oath.

He said the investigation was at a critical stage, and they hoped to complete it by the end of June, albeit that they were still receiving further information from whistleblowers.

Earlier, Mothibi informed the committee that out of the total Covid-19 expenditure of R126.7-billion between April 2020 and the end of March 2021, it was investigating procurement worth R14.3-billion.

Out of this R14.3-billion, more than R600-million had already been referred to the Special Tribunal for recovery.

The SIU is investigating 4 177 contracts for Covid-19 related services. These contracts were awarded to 2 251 service providers. In total, 40% of these contracts have been finalised, 54% are currently being assessed and 6% have yet to commence.

Thus far, the SIU has referred 88 state officials for disciplinary action, while 44 have been referred to the National Prosecuting Authority.

The SIU said it aimed to finalise the investigations into Covid-19-related procurement by August.

Meanwhile, the DA announced that it would lay criminal charges against Mkhize regarding Digital Vibes.

"Considering the clear violation of the law, the DA will be laying criminal charges against minister Mkhize and health Director-General Dr Sandile Buthelezi with the South African Police Service [on Thursday]. Over and above the SIU probe, a criminal investigation needs to ensue," DA MP and spokesperson on health Siviwe Gwarube said in a statement.