WASHINGTON - An FBI lawyer is suspected of altering a document related to surveillance of a former Trump campaign adviser, a person familiar with the situation said Friday.

President Donald Trump, who has long attacked as a "hoax" and a "witch hunt" the FBI's investigation into ties between Russia and his 2016 presidential campaign, immediately touted news reports about the allegations to assert that the FBI had tried to "overthrow the presidency."

The allegation is part of a Justice Department inspector general investigation into the early days of the FBI's Russia probe, which was ultimately taken over by special counsel Robert Mueller and resulted in charges against six Trump associates and more than two dozen Russians accused of interfering in the election. Inspector General Michael Horowitz is expected to release his report on Dec. 9. Witnesses in the last two weeks have been invited in to see draft sections of that document.

The release of the inspector general report is likely to revive debate about the investigation that has shadowed Trump's presidency since the beginning. It is centered in part on the FBI's use of a secret surveillance warrant to monitor the communications of former Trump campaign adviser Carter Page.

"This was spying on my campaign - something that has never been done in the history of our country,'' Trump told "Fox & Friends" on Friday. "They tried to overthrow the presidency."

The allegation against the lawyer was first reported by CNN. The Washington Post subsequently reported that the conduct of the FBI employee didn't alter Horowitz's finding that the surveillance application of Page had a proper legal and factual basis, an official told the Post, which said the lawyer was forced out.

A person familiar with the case who was not authorized to discuss the matter by name and spoke to AP only on the condition of anonymity confirmed the allegation. Spokespeople for the FBI and the inspector general declined to comment Friday.

The FBI obtained a secret surveillance warrant in 2016 to monitor the communications of Page, who was never charged in the Russia investigation or accused of wrongdoing. The warrant, which was renewed several times and approved by different judges in 2016 and early 2017, has been one of the most contentious elements of the Russia probe and was the subject of dueling memos last year issued by Democrats and Republicans on the House Intelligence Committee.

Republicans have long attacked the credibility of the warrant application since it cited information derived from a dossier of opposition research compiled by Christopher Steele, a former British spy whose work was financed by Democrats and the Hillary Clinton campaign.

"They got my warrant - a fraudulent warrant, I believe - to spy on myself as a way of getting into the Trump campaign," Page said in an interview with Maria Bartiromo on Fox's "Mornings with Maria" "There has been a continued cover"-up to this day. We still don't have the truth, but hopefully, we'll get that soon."

FBI Director Chris Wray has told Congress that he did not consider the FBI surveillance to be "spying" and that he has no evidence the FBI illegally monitored Trump's campaign during the 2016 election. Wray said he would not describe the FBI's surveillance as "spying" if it's following "investigative policies and procedures."

Attorney General William Barr has said he believed "spying" did occur, but he also made clear at a Senate hearing earlier this year that he had no specific evidence that any surveillance was illegal or improper. Barr has appointed U.S. Attorney John Durham to investigate how intelligence was collected, and that probe has since become criminal in nature, a person familiar with the matter has said.

But Trump insists that members of the Obama administration "at the highest levels" were spying on his 2016 campaign. "Personally, I think it goes all the way. ... I think this goes to the highest level,'' he said in the Fox interview. "I hate to say it. I think it's a disgrace. They thought I was going to win and they said, 'How can we stop him?'"