WASHINGTON—Attorney General William Barr quickly and sharply disputed a watchdog’s key finding that the Federal Bureau of Investigation was legally justified in opening its Russia inquiry, further enmeshing the Justice Department in a partisan battle over the bureau’s probe of President Trump and his associates.



Mr. Barr’s remarks also suggested that a federal prosecutor he appointed to take a separate look at the investigation would come to a different conclusion.

Michael Horowitz, the Justice Department’s inspector general, determined in a report released Monday that the FBI had adequate basis in 2016 to open its investigation and found no direct evidence that political bias influenced the inquiry. But Mr. Barr pointed to the report’s more scathing findings of FBI errors and missteps, echoing Mr. Trump’s own long-held complaints about the investigation of his presidential campaign.

“The inspector general’s report now makes clear that the FBI launched an intrusive investigation of a U.S. presidential campaign on the thinnest of suspicions that, in my view, were insufficient to justify the steps taken,” Mr. Barr said in a lengthy statement issued immediately following the report’s release. “Nevertheless, the investigation and surveillance was pushed forward for the duration of the campaign and deep into President Trump’s administration.”

Mr. Barr said that FBI officials, in their rush to obtain surveillance warrants, had “omitted critical exculpatory facts from their filings and suppressed or ignored information negating the reliability of their principal source.”