Washington — The Justice Department's internal watchdog said a highly anticipated report on the department's use of secret surveillance warrants during the Russia investigation is "nearing completion" and will likely be released publicly, according to a letter obtained by CBS News.

Inspector General Michael Horowitz wrote to congressional leaders on Thursday with an update on his investigation into alleged abuses of warrants obtained under the Foreign Intelligence Surveillance Act (FISA). Horowitz said he expects the report "will be released publicly with few redactions," but declined to provide a timeline.

"I can report to you that the process is ongoing and nearing completion, and we are working through these issues constructively with both the Department and the FBI," Horowitz wrote. "The goal from my standpoint is to make as much of our report public as possible."

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Read the letter here

In March 2018, the inspector general's office opened a review into the origins of the counterintelligence investigation that eventually led to the Mueller probe. Specifically, Horowitz said his investigators would look into how the Justice Department and FBI obtained FISA warrants to surveil a "certain U.S. Person," reportedly referring to former Trump campaign aide Carter Page.

The inspector general's report is separate from the probe being conducted by U.S. Attorney John Durham, who is also looking at the early days of the Russia investigation. Durham is examining whether the government's intelligence collection efforts related to Trump associates were lawful and appropriate, including during the campaign and after President Trump was inaugurated.

Durham's investigation, which is ongoing, features prominently in the events at the center of House Democrats' impeachment inquiry into the president. On his July 25 phone call with Ukrainian President Volodymyr Zelensky, Mr. Trump urged him to cooperate with Durham's investigation, specifically regarding debunked allegations of Ukrainian involvement in election interference in 2016.

Since Horowitz indicated in his letter on Thursday that he expects the report to have minimal redactions, he said he does not "anticipate a need to prepare and issue separate classified and public versions of the report."

In September, Horowitz informed Congress that his office was in the process of finalizing the report and that he had provided a draft copy of it to the FBI and Department of Justice, including Attorney General William Barr.