Trump accuses Obama of 'tapping' his phone during campaign

Trump leveled the charges in a flurry of tweets shortly after dawn, amid an avalanche of recent revelations about communications between Russian officials and some of his senior aides, including Attorney General Jeff Sessions.

Trump repeatedly has denied having any personal ties to the Kremlin, and his aides have denied or played down contacts with Russian officials.

But the accusations have continued amid almost daily leaks to the press that have revealed new details about links between Moscow and senior Trump officials. 

One such revelation earlier this week in the Washington Post about a meeting between Sessions and Russian Ambassador Sergey Kislyak prompted the Republican former US senator to recuse himself from any investigations into the Trump campaign's possible Russia ties.

Sessions had told a Senate committee under oath that he "did not have communications with the Russians," but reporters found that he had actually met the Russian ambassador twice in the months before taking up his post as attorney general, America's top law enforcement officer.

Trump has expressed his displeasure over the charges -- and the barrage of leaks that led to them --  lashing out in tweets Friday directed at the top Democrats in the Republican-led Congress -- Senator Chuck Schumer and Representative Nancy Pelosi.

The businessman-turned-politician, who has accused his political foes of conducting "a total witch hunt" on Saturday directed his Twitter tirade at his Democratic predecessor.

Since US intelligence took the unprecedented step of publicly accusing Russia of trying to swing the November election in Trump's favour, questions have swirled about whether some in Trump's campaign colluded with Moscow.