Police are looking into investigative journalists Jacques Pauw and Pieter-Louis Myburgh, who have both written about alleged corrupt relationships involving President Jacob Zuma.
However, police say no case against the two has been opened.
The matter may, therefore, have been registered by police in another manner.
Myburgh, a News24 investigative journalist, wrote the book The Republic of Gupta and has probed, and written about, several alleged corrupt relationships involving government officials.
He was part of the team from News24, AmaBhungane and Daily Maverick who were last month crowned overall winners of the Vodacom Journalist of the Year awards for their work on the #GuptaLeaks, which exposed the extent of the influence that the controversial Gupta family has over South African public enterprises.
Pauw is the author of the book The President's Keepers.
They have both, according to their legal representatives, been requested to make statements at the Durban North police station in a matter apparently relating to material they have written about.
A police officer, based in Durban North, indicated to their attorneys that he was the investigating officer in the matter.
However, national police spokesperson Vishnu Naidoo on Tuesday said no case had been opened, and that Pauw and Myburgh were not under investigation.
News24 then provided him with the surname and cellphone number of the apparent investigating officer.
It is also understood the matter may not have been registered as a case to be investigated, but as an inquiry.
Asked if this was the case, Naidoo said on Wednesday: "Due to the sensitive nature of such matters we are unable to discuss them in the public domain."
News24 called the cellphone of the apparent investigating officer on Tuesday.
A man who answered said he would pass a message on to the officer. The officer did not return calls, nor respond to an SMS on Wednesday.
Previous attempt for arrest warrant
Pauw on Tuesday said he was told about potential charges he could face about two weeks ago, when he heard that a police officer had tried to secure a warrant in Pietermaritzburg for his arrest.
The officer had not managed to do so.
Last month, Pauw had said the warrant related to five charges, including fraud and crimen injuria.
He had not been sure whether police would try again with another magistrate.
He said on Tuesday that the investigating officer in the case would not divulge what was being probed.
"Whatever he brings, we will defend it," Pauw said.
On Tuesday, the lawyers representing both Pauw and Myburgh - Willem de Klerk Attorneys - sent a letter to a colonel, the investigating officer, who they said on Monday had spoken to Willem de Klerk about the matter.
The letter is headed: "Criminal investigation: Jacques Pauw and Pieter-Louis Myburgh."
'Potential suspects for what they have written'
"From the said telephone discussions it appears that Mr Pauw is regarded as a potential suspect related to material contained in his book The President's Keepers," the letter said.
"It further appears that Mr Pieter-Louis Myburgh is a potential suspect based on an article or articles he may have authored which appeared in the news media."
It said the investigating officer had not been willing to disclose further details about what was being investigated.
Requested to provide information to police
The letter confirmed a request by the investigating officer that Pauw and Myburgh go to the Durban North police station to answer questions, or to possibly make statements or do both.
"Our clients are not at this stage willing to answer questions or make statements but would prefer for the investigation to be completed first," the letter stated.
"If you require our clients to depose to affidavits stating as much, we are happy to oblige and will send such affidavits to you as soon as possible."
Pauw and Myburgh's decision not to make statements yet was based on legal advice and their Constitutional rights.
"It does not imply that they are uncooperative in the matter," the letter stated.
Pauw and Myburgh, it said, would give their full cooperation if the National Prosecuting Authority decided to act against them.
"Our clients are desirous to finalise the matters under investigation in the spirit of co-operation," the letter read.
"If they are required to appear in any criminal court they will fully co-operate without the need for arrest."
News24 editor Adriaan Basson said the police investigation amounted to attempted intimidation.
'Clear attempt at intimidation'
"It is outrageous that the cops are going after journalists when corrupt politicians and captured business people roam free," he said.
"We will oppose any attempts to bring criminal charges against Myburgh. This is a clear attempt to try and intimidate us from doing our jobs. We won't be deterred."
The Hawks were also investigating material in Pauw's book.
They previously said they were investigating the leak of classified information that ended up being published in it.
This was after a case was opened by the State Security Agency (SSA).
The SSA had also demanded that the book be withdrawn.
Previously the South African Revenue Service (SARS) said it was considering legal action in relation to Pauw's book.
This, after the Sunday Times carried an extract of his book which alleged that Zuma received monthly payments of R1m from controversial tender mogul Roy Moodley, without declaring it to SARS. -- News24Suggest a correction