Trump demands Justice Department to probe if it or FBI spied on his election campaign

President Donald Trump has asked the US Department of Justice to investigate whether the FBI spied on his 2016 election campaign for "inappropriate purposes" on the orders of people in the Obama administration.

Trump's move came after it was reported that the FBI dispatched a confidential source to speak with some aides to Trump's presidential campaign about its possible ties to Russia, according to US media reports.

"I hereby demand, and will do so officially tomorrow, that the Department of Justice look into whether or not the FBI/DOJ infiltrated or surveilled the Trump Campaign for Political Purposes - and if any such demands or requests were made by people within the Obama Administration!" Trump tweeted.

Trump's latest demand came amid a series of tweets yesterday denouncing a "witch hunt" that, he said, had found no collusion by his campaign with Russia.

US Deputy Attorney-General Rod Rosenstein said action would be taken if any infiltration was found.

"If anyone did infiltrate or surveil participants in a presidential campaign for inappropriate purposes, we need to know about it and take appropriate action," Rosenstein said in a statement.

There is already an investigation into all aspects relating to Trump's campaign for the 2016 election and whether Russia tried to influence the outcome.

There is an ongoing investigation led by Special Counsel Robert Mueller into Russia's efforts to interfere in the 2016 US election, whether there was any collusion between the Kremlin and Trump's election campaign and whether the president tried unlawfully to obstruct the inquiry.

Trump has constantly attacked the inquiry.

Trump first made the accusation that the FBI had sent a spy into his campaign team on Friday.

"It took place very early on, and long before the phony Russia Hoax became a 'hot' Fake News story," Trump had tweeted, adding: "If true - all time biggest political scandal!"