The US Department of Justice has said it will investigate whether the FBI spied on Donald Trump’s presidential campaign for political motives, following the US president’s call for an inquiry.

“If anyone did infiltrate or surveil participants in a presidential campaign for inappropriate purposes, we need to know about it and take appropriate action,” Deputy Attorney General Rod Rosenstein said in a statement late on Sunday.

Trump had demanded that the Justice Department look into possible infiltration or surveillance by the FBI or the DOJ itself of his 2016 campaign, stressing that it was essential to probe if someone from his predecessor Barack Obama’s administration had ordered such a request.

“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!,” the US president said on Twitter on Sunday morning.

The probe comes amid an ongoing investigation, headed by Special Counsel Robert Mueller, into alleged collusion between the Russian government and Trump’s 2016 election campaign.

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! — Donald J. Trump (@realDonaldTrump) May 20, 2018

In a series of tweets on Sunday, Trump criticised Mueller’s investigation, calling it a “witch-hunt” and asserting that it had not found any collusion with Russia.

‘No evidence’

On May 17, Mueller was appointed by the US Justice Department to look into possible Russian interference into the 2016 US elections, which Trump won.

So far, the Mueller team has indicted a total of 22 people and companies.

Bruce Fein, a former US associate deputy attorney general, says there are valid reasons for the Russian investigation as too many people from Trump’s campaign team associated with foreign officials.

He told Al Jazeera that Trump’s suggestion that the FBI “targeted his campaign because of hostility towards his political ambitions would be a real problem”.

“We don’t have any evidence at present that suggests that the FBI actually infiltrated the campaign under false pretences, had somebody working for Trump and had access into getting confidential communication that wouldn’t have been obtained if they weren’t part of the campaign itself,” said Fein, speaking from Washington, DC.

Last year, the Republican president also accused Obama of tapping his phones during the late stages of the election campaign but offered no evidence to support the allegation.

“He’s so reckless in his allegations that you can’t even sift the wheat from the chaff,” said Fein.

In November 2016, Trump defeated rival Hillary Clinton in an election tainted by an email scandal, following claims that the Democratic candidate used her private server while she was secretary of state.