US President-elect Donald Trump has reprised his election campaign attacks on Hillary Clinton, declaring her "guilty as hell" on social media and deriding her supporters' criticism of how the FBI handled an investigation into her emails.

The US Justice Department announced yesterday it would investigate an FBI decision to launch an inquiry into Mrs Clinton's emails shortly before the November 8 election, a move she has blamed as a factor in her defeat.

Mr Trump took to Twitter overnight to assert Mrs Clinton should have “never been allowed to run” for President of the United States.

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

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

Mrs Clinton has not responded to Mr Trump's tweets.

Mr Trump had often led crowds in chants of "lock her up!" during the 2016 election campaign, accusing Mrs Clinton of illegal conduct over her use of a private email server for official correspondence while she was secretary of state under President Barack Obama.</p>

In a debate in October, the Republican real estate developer vowed Mrs Clinton would "be in jail" over the matter if he became president, but later said he would not pursue prosecution.

Some of the Clinton emails were determined to contain classified information. The FBI ultimately decided not to refer her case for prosecution.

Democrats said FBI Director James Comey's announcement of the new inquiry into the emails damaged her standing with voters right before the election, and he faced complaints that his moves were politically motivated.

Brian Fallon, Mrs Clinton's spokesman, told MSNBC on Thursday that Mr Comey's actions "cried out for an independent review."