President Jacob Zuma has directed the Special Investigating Unit (SIU) to conduct a probe into corruption in the South African Police Service (SAPS).

The probe, mainly into procurement, "originates from a referral" by police watchdog, the Independent Complaints Directorate (ICD), the Presidency said in a statement on Thursday.

The investigation has the "full support" of the National Police Commissioner General Bheki Cele.

The proclamation was gazetted seven days after former national police commissioner Jackie Selebi was sentenced to 15-years in jail for corruption.

It also comes after revelations about a "dodgy" multi-million rand property deal signed by Cele.

The R500-million property deal would see police headquarters move to the 18-storey Middestad Sanlam centre in Pretoria, which was owned by billionaire businessman Roux Shabangu, reported the Sunday Times last month.

According to the report, the deal was allegedly not treated as a tender, violating Treasury regulations that all government contracts worth over R500 000 go through a bidding process.

The Presidency said that the SIU would look into the "procurement of and contracting for goods, works or services including leased accommodation, by or on behalf of the Service".

It includes payments that may have been made with "undeclared conflicts of interest" or "conducted or facilitated by the manipulation of the service's supply chain management, procurement or information system management processes" or "in collusion with or through the intervention of the service's personnel".

The probe also extends to "unlawful or irregular conduct by the service's personnel, the service's suppliers and service providers or third parties relating to any one or more of the aforementioned allegations."

The SIU is an independent statutory body that is accountable to Parliament and the President.

The Congress of South African Trade Unions (Cosatu) welcomed the investigation, saying that it was "in line" with what the union federation has in the past called for.

"We urge the [SIU] to leave no stone unturned to uncover any corruption or misuse of public funds in such areas as the procurement of goods and services, contracts signed, or not signed, by officials or officers with an undeclared conflict of interest and unauthorised, irregular, wasteful or fruitless expenditure in any branch of the SAPS," said spokesperson Patrick Craven in a statement.

Cosatu has taken a tough stance against corruption, even clashing with its alliance partner, the African National Congress, in its calls for the government to take tougher action against ministers who are linked to corrupt activity.

"Allegations of corruption must be either proved or disproved. Everyone is innocent until proved guilty, but this can only be established when the evidence has been thoroughly investigated," Craven said.