The FBI was justified in opening an investigation into ties between the Trump presidential campaign and Russia and did not act with political bias, despite “serious performance failures” up the bureau’s chain of command, a highly anticipated report has said.

The findings of the Justice Department’s inspector general undercut President Donald Trump’s claim that he was the target of a “witch hunt”.

The report revealed for the first time that the FBI had also sent an informant to record a conversation with a “high-level Trump campaign official”, who was not considered a subject in the Russia probe. The official was not identified by name.

The report also found the bureau was justified in eavesdropping on a former Trump adviser and that there was no documented or testimonial evidence of any political bias.

Mr Trump, in remarks at the White House shortly after the report’s release, claimed that it showed “an attempted overthrow and a lot of people were in on it”.

Its nuanced conclusions deny a clear-cut vindication for Mr Trump’s supporters or critics. It rejects theories and criticism spread by the president and his supporters while also finding errors and misjudgments likely to be exploited by Republican allies as the president faces a probable impeachment vote this month.

Mr Trump has sought to downplay expectations, saying repeatedly that he was more eager for the report of John Durham, the hand-picked prosecutor selected by attorney general William Barr to conduct a separate review of the Russia probe.

Mr Barr rejected the inspector general’s conclusion that there was sufficient evidence to open the investigation.

“The inspector general’s report now makes clear that the FBI launched an intrusive investigation of a US presidential campaign on the thinnest of suspicions that, in my view, were insufficient to justify the steps taken,” he said in a statement.

The inspector general identified 17 “significant inaccuracies or omissions” in applications for a warrant from the secretive Foreign Intelligence Surveillance Court to monitor the communications of former Trump campaign adviser Carter Page and subsequent warrant renewals.

The errors, the watchdog said, resulted in “applications that made it appear that the information supporting probable cause was stronger than was actually the case”.

FBI director Chris Wray said the problems found by the report are “unacceptable” and “unrepresentative of who we are as an institution”.

The report’s release, coming on the day a House Judiciary Committee impeachment hearing centred on the president’s interactions with Ukraine, brought fresh attention to the legal and political investigations that have entangled the White House from the moment Mr Trump took office.

The investigation, which was ultimately taken over by special counsel Robert Mueller, began in July 2016 after the FBI learned that a former Trump campaign aide, George Papadopoulos, had been saying before it was publicly known that Russia had dirt on Democratic opponent Hillary Clinton in the form of stolen emails.

Those emails, which were hacked from Democratic email accounts by Russian intelligence operatives, were released by WikiLeaks in the weeks before the election in what US officials have said was an effort to harm Ms Clinton’s campaign and help Mfr Trump.

The report said the FBI was authorised to open the investigation about the basis for opening the investigation to protect against a national security threat.

Months later, the FBI sought and received the Page warrant. Officials were concerned that Mr Page was being targeted for recruitment by the Russian government, although he has denied wrongdoing and has never been charged with a crime.