The US Justice Department's internal watchdog said it would examine whether FBI Director James Comey publicly handled the Clinton investigation.

The US Department of Justice Inspector General will review broad allegations of misconduct involving the FBI's investigation of Hillary Clinton's email practices.

It will include the bureau's controversial decision shortly before the election to announce the probe had resumed, the Inspector General announced.

The probe will be wide ranging - encompassing the FBI's various public statements on the matter, whether its deputy director should have been recused and whether Department of Justice or FBI employees leaked non-public information, according to a news release from Inspector General Michael Horowitz.

CARLOS BARRIA Comey delivered an unusual public statement for an FBI chief by chastising Clinton and her aides as "extremely careless."

Lawmakers and others had called previously for the inspector general to probe the FBI's pre-election actions when it came to the Clinton probe, alleging that FBI Director James Comey bucked longstanding policies with his communications about the case and that information seemed to have leaked inappropriately - perhaps to former New York City Mayor Rudy Giuliani.

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JONATHAN ERNST/REUTERS The probe will look into whether FBI Director James Comey properly followed department policies ahead of the US election.

During his announcement, Comey delivered an unusual public statement for an FBI chief by chastising Clinton and her aides as "extremely careless."

AFP In July 2016, the Federal Bureau of Investigation said it would not recommend charges over Hillary Clinton's use of a private email server as secretary of state.

It will also review the two letters he sent to Congress about the case in the final days before the 2016 election.

Clinton and her aides said the disclosure of "new" emails - found on a laptop belonging to Anthony Weiner, the estranged husband of Clinton aide Huma Abedin - less than two weeks before Election Day hurt her in several battleground states.

Comey's action prompted outrage from Clinton and other Democrats who said it needlessly placed her under suspicion when the FBI didn't even

Horowitz said in a news release he would explore those topics and more, though he would not re-litigate whether anyone should have faced charges.

"The review will not substitute the OIG's judgment for the judgments made by the FBI or the Department regarding the substantive merits of investigative or prosecutive decisions," the news release said, using an acronym for the Office of the Inspector General.

The FBI's probe into whether Clinton mishandled classified information by using a private email server when she was secretary of state has long been controversial and politically charged.

Perhaps most notably, Comey on October 28 - after previously announcing publicly that he was recommending no charges in the case - sent a letter to congressional leaders telling the agents had resumed the Clinton probe after finding potentially relevant information in an unrelated case.

The day before, senior Justice leaders had warned Comey not to send the letter because it violated two longstanding department policies - discussing an ongoing investigation and taking any overt action on an investigation so close to an election.

At the time, early voting had already begun and it was less than two weeks before the election.

Comey sent a second letter to Congress, just days before the election, saying that the investigation was complete and he was not changing the decision he had made in July to bring no charges against Clinton.

But the damage - in the minds of Clinton supporters, at least - had been done. Clinton has blamed the renewed FBI inquiry for blunting her momentum in the last weeks of the presidential election.

Horowitz wrote that he would explore "allegations that Department or FBI policies or procedures were not followed" in connection with both letters, but his probe would extend beyond that.

He wrote that he also would explore "allegations that Department and FBI employees improperly disclosed non-public information" - which is perhaps a reference to Giuliani, who seemed to claim at one point he had insider FBI knowledge. And he wrote that his inquiry would extend back to Comey's July announcement that he was recommending the Clinton case be closed without charges.

In that instance, Comey took the unusual step of criticising Clinton and her aides as "extremely careless" in their treatment of classified material, even as he said no reasonable prosecutor would charge them.

His comments drew criticism from some in the legal world, who said it was unfair for him to opine on a person he was not giving the opportunity to defend herself in court.