Trump under investigation for obstruction of justice: Report

US President Donald Trump is being investigated by special counsel Robert Mueller for possible obstruction of justice, the Washington Post reported on Wednesday, citing unidentified officials.

Mueller is investigating allegations of Russian interference in the 2016 US presidential election and possible collusion with the Trump campaign. Former FBI Director James Comey told Congress last week he believes he was fired by Trump to undermine the agency's Russia probe.

Trump caused an uproar when he fired Comey on 9 May. Comey had told Congress that the FBI was investigating possible links between Trump campaign officials and the Russian government, which US intelligence agencies accuse of hacking the Democratic National Committee’s emails last year in a bid to influence the election against Hillary Clinton.

Associates of Comey revealed an unclassified memo in which the former FBI director describes a conversation with Trump, with the president asking him to end an FBI investigation into former national security adviser Michael Flynn.

Trump said in mid-May the special counsel’s probe would show there was "no collusion" between his campaign and a foreign power.

"As I have stated many times, a thorough investigation will confirm what we already know – there was no collusion between my campaign and any foreign entity," he said in a statement released by the White House.

"I look forward to this matter concluding quickly. In the meantime, I will never stop fighting for the people and the issues that matter most to the future of our country."