US President-elect Donald Trump has hit out at President Barack Obama over 'inflammatory' comments he has made during the Republican's transition period.

Trump said he had been expecting a smooth transition to his role as president, but suggested incumbent Obama had made it a more difficult experience.

"Doing my best to disregard the many inflammatory President O statements and roadblocks.Thought it was going to be a smooth transition - NOT!," Trump wrote on Twitter.

The president-elect's team has butted heads with the White House over the past few weeks, with staffers hitting out at each other in what has become and increasingly fractured transition process.

On 15 December, Trump hit out at White House press secretary Josh Earnest, telling a rally of supporters Earnest was "a foolish guy".

"This foolish guy, Josh Earnest, I don't know," he told the audience. "You know, having the right press secretary is so important because he's so bad the way he delivers a message. He can deliver a positive message and it sounds bad. He could say ladies and gentlemen, today we have totally defeated ISIS [Islamic State], and it wouldn't sound good."

Trump was responding to a dig made by Earnest, who suggested the Republican was well aware of Russia being involved in hacking.

Earnest had told the press: "It is just a fact – you all have it on tape – that the Republican nominee for president was encouraging Russia to hack his opponent, because he believed that would help his campaign," Earnest had said, prompting a backlash from Trump's team.

"It is not a controversial statement. I'm not trying to be argumentative. But I am trying to acknowledge a basic fact."

Obama's staffers have also hit out at Trump's team by mocking their boast of saving more than 1,000 jobs in Indiana, suggesting they would need to do a lot more to reach the same job creation goals as Obama. and stating Trump knew about Russia hacking the Democrats.

Both Obama and Trump have stated they wish the transition to be smooth, but with several weeks still to go until the inauguration, it is clear both sides are intent on continuing to trade blows, with their different opinion on issues such as the recently-seized US Navy drone by China prompting an opposite reaction from the incumbent and incoming presidents.