Trump aims criticism towards Clinton once again as FBI investigation launched

US president-elect Donald Trump went on the offensive against Hillary Clinton once again, saying his former rival was "guilty as hell" following the launch of an investigation into the FBI's actions during the election campaign.

Trump had spoken very little about Clinton since his widely unexpected victory over the Democrat in November, but took to Twitter once again to denounce her, just one week before he was due to enter the White House.

FBI director James Comey's decision to open the investigation into Clinton's use of a private email server just 11 days before the election shook up the race.

"What are Hillary Clinton's people complaining about with respect to the FBI," Trump tweeted. "Based on the information they had she should never have been allowed to run - guilty as hell."

"They were VERY nice to her. She lost because she campaigned in the wrong states - no enthusiasm!" Trump added.

On Thursday, the Inspector General of the Department of Justice Michael Horowitz said he would be investigating "certain actions" by the FBI and the department relating to the election

Clinton's public appearances had been few and far between since she was defeated by Trump, with very few sightings of the former secretary of state apart from one speech given at a charity fundraiser in December.

She was cleared of any wrongdoing just days before the 8 November election, but Trump's latest comments brought the issue to light again.