Palm Beach, United States: The White House on Sunday called for Congress to follow up on Donald Trump’s explosive and unsubstantiated allegation that Barack Obama tapped his phone during last year’s election campaign.

Twenty-four hours after Trump’s incendiary claim, his aides scrambled to limit the political fallout -- admitting it was still unproven and calling on Congress to investigate.

Citing still undefined ‘reports’ of ‘politically motivated investigations,’ press secretary Sean Spicer said Trump was calling on Congress to ‘determine whether executive branch investigative powers were abused in 2016.’

Trump spokeswoman Sarah Sanders echoed those comments.

‘If this happened,’ she told ABC, ‘this would be the greatest abuse of power and overreach that has ever occurred in the executive branch.’

President Barack Obama, via a spokesman, denied the allegation as ‘simply false.’

US presidents cannot legally order such wiretaps, which require the approval of a federal judge and reasonable grounds for suspicion.

Obama’s director of national intelligence James Clapper told NBC there was ‘no such wiretap activity mounted against the president-elect at the time as a candidate or against his campaign.’

Trump levelled his charges in a string of tweets early Saturday, at the end of a week in which his administration was battered by controversy over links between his advisors and Russian officials.

The Republican’s comments appeared to have been based on unverified claims made by the right-wing Breitbart News outlet.

Trump’s claim reflected his fury that good reviews of his maiden speech to Congress on Tuesday were overtaken by a series of revelations about aides’s meetings with Russian officials.

The president was also said to be angry that Attorney General Jeff Sessions recused himself from any campaign or Russia-related investigations.

Sessions’s recusal came after it emerged that he did not disclose two meetings with Moscow’s ambassador in Washington.

Amid this and several other revelations of Trump aides holding meetings with Russian officials, the White House has denied allegations of collusion.

US intelligence agencies have concluded that Russian President Vladimir Putin approved a campaign to tilt last November’s presidential election in Trump’s favour.

Former CIA director Leon Panetta accused Trump of diversionary tactics.

‘They are trying to obfuscate and trying to cover up. They are trying to somehow raise other issues,’ he told CBS.

‘In the end, it is going to be the truth that will determine what is involved here, and not tweets, but the truth.’

Democrats and a growing number of Republicans in Congress have called for the appointment of a special prosecutor.

With already low approval ratings, Trump could do without another scandal in his young presidency.

Republicans have largely stood behind him, hoping he will enact tax cuts and other policies they favour.

But some Republican lawmakers appear to be losing patience with the drama of Trump’s presidency.

‘We are in the midst of a civilization-warping crisis of public trust,’ said Senator Ben Sasse.

He added that Trump’s allegations of wiretapping ‘demand the thorough and dispassionate attention of serious patriots.’