Trump names former Iraq and Afghanistan general Mattis as defence secretary

US president-elect Donald Trump is continuing to form his administration for when he takes over from Barack Obama on 20 January of next year, naming former marine James Mattis, known as "Mad Dog", as his defence secretary.

Mattis served in Iraq and Afghanistan before retiring, and has since been highly critical of president Barack Obama's policy in the Middle East.

Trump made the announcement in Ohio as he has been making his way across various US states on a victory tour to thank the millions who voted for him.

"I will not tell you that one of our great great generals, don’t let it outside, we are going to appoint Mad Dog Mattis as our secretary of defence and we're not announcing it until Monday so don’t tell it to anybody," Trump told supporters at a rally in Cincinnati on Thursday evening.

Trump's speech in the state where he claimed a key victory over Hillary Clinton was very much a reversion back to his rambunctious campaign behaviour, rather than the distinctly more presidential demeanour he has held since his win last month.

There were swipes in the direction of Clinton, who has recently backed Jill Stein's efforts to secure a recount in three key states. Trump also aimed another strike in the direction of the US media, with the crowd joining in on the discontent shown towards the section of reporters at the rally.

Unlike many of Trump's appointments so far, the pick of Mattis is expected to be welcomed by those in Washington, particularly from those on the Republican side who are hoping that Mattis will be able to moderate the president-elect, and national security council adviser Michael Flynn.