An FBI agent is reportedly being investigated for allegedly altering a document in the controversial probe of Trump campaign aides.

CNN published the exclusive report on Thursday based on sources familiar with the matter.

According to the report, Department of Justice Inspector General Michael Horowitz turned over evidence of the altered document to federal prosecutor John Durham.

The document was altered in a "substantive" manner, but it is unclear whether it would have changed the origin of the FISA probe.

Durham was appointed by Attorney General William Barr to investigate the origins of the FISA probe into the Trump campaign in 2016.

The controversial investigation of Trump campaign aide Carter Page has come under intense scrutiny as Republican allies of the president accused former members of the Obama administration of inappropriately using the power of the government to surveil the campaign.

Former Obama era national security advisor Susan Rice are among those claiming that there was no political motivation involved in the investigation, and that the probe was conducted appropriately.

Details of the allegedly altered document will be included in the report from Horowitz to be released in December.

CNN admitted in its report that the altering of documentation would help "fuel" claims from the allies of the president that the FBI was improperly abusing their power to target then-candidate Trump.

"This is exactly what people close to the president have been saying, that the FBI committed wrongdoing in starting this investigation," said CNN's Manu Raju.

Here's CNN's video on the report: