FBI director James Comey has reportedly dismissed Donald Trump's claims that his phone was tapped during last year's presidential campaign.

Key points: Trump accused Obama of wire-tapping his phones during the 2016 election

Trump accused Obama of wire-tapping his phones during the 2016 election The FBI has reportedly dismissed the claim

The FBI has reportedly dismissed the claim House Democratic leader calls it "a wrap-up smear" and "tool of authoritarianism"

Mr Trump has turned to Congress for help in finding evidence to support his unsubstantiated claim that former president Barack Obama had Trump Tower's telephones tapped during the election, with the White House saying the issue should be looked at as part of the ongoing congressional probe into Russia's influence on the US election.

A US official told the Associated Press that the FBI had asked the Justice Department to dispute Mr Trump's allegations.

The New York Times reported that senior American officials said Mr Comey had argued that the claim must be corrected by the Justice Department because it falsely insinuated that the FBI broke the law.

Mr Obama's director of national intelligence, James Clapper, said nothing matching Mr Trump's claims had taken place.

"Absolutely, I can deny it," said Mr Clapper, who left government when Mr Trump took office in January. Other representatives for the former president also denied Mr Trump's allegation.

Under US law, a federal court would have to have found probable cause that the target of the surveillance was an "agent of a foreign power" in order to approve a warrant authorising electronic surveillance of Trump Tower.

Justice Department spokeswoman Sarah Isgur Flores declined to comment, and an FBI spokesman also did not comment.

White House spokesman Sean Spicer said Mr Trump and administration officials would have no further comment on the issue until Congress had completed its probe, potentially heading off attempts to get Mr Trump to explain his accusations.

"Reports concerning potentially politically motivated investigations immediately ahead of the 2016 election are very troubling," Mr Spicer said in a statement.

"President Trump is requesting that as part of their investigation into Russian activity, the congressional intelligence committees exercise their oversight authority to determine whether executive branch investigative powers were abused in 2016."

Asked to elaborate on Mr Spicer's statement in an interview with ABC News America, White House principal deputy press secretary Sarah Sanders responded: "If this happened, this would be the greatest abuse of power and overreach that's probably ever occurred in the executive branch."

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When reporter Martha Raddatz asked about Ms Sanders' use of the word "if" when Mr Trump had "stated it as fact", Ms Sanders said she would "let the President speak for himself".

"I think that we should get definitive answers. I think we need to put out hard facts that show that this happened," Ms Sanders said.

Trump urged to explain allegations

Mr Trump made the wire-tapping accusation in a series of early morning tweets, amid expanding scrutiny of his campaign's ties to Russia.

In his tweets, Mr Trump suggested Mr Obama was behind a politically motivated plot to upend his campaign.

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He compared the alleged events to "Nixon/Watergate" and "McCarthyism!", calling Mr Obama a "Bad (or sick) guy".

After Mr Trump's well-received speech to Congress on Tuesday, the tweets reflected the President's growing frustration with the swirling allegations about his advisers' ties to Russia, which are under FBI investigation, and his team's inability to overcome them.

Mr Trump said in the tweets that he had "just found out" the information, though it was unclear whether he was referring to a briefing, a conversation or a media report.

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The President has in the past tweeted about unsubstantiated and provocative reports he reads on blogs or conservative websites.

The morning tweets stand out, even for the perpetually piqued Mr Trump, given the gravity of the charge and the strikingly personal attack on the former president.

Mr Trump spoke as recently as last month about how much he liked Mr Obama and how much they got along, despite their differences.

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Representative Adam Schiff of California, the senior Democrat on the House Intelligence Committee, said in a statement that Mr Trump was making "the most outlandish and destructive claims without providing a scintilla of evidence to support them".

Meanwhile, senator Ben Sasse urged Mr Trump to explain what he knew about the wire-tapping allegations, "ideally to the full public, and at a bare minimum to the US Senate".

On Sunday, Mr Obama's press secretary Josh Earnest and House Democratic leader Nancy Pelosi accused Mr Trump of levelling the allegations against the former president to distract from the attention being given to campaign-season contacts by Trump aides with Russia.

"It's called a wrap-up smear. You make up something. Then you have the press write about it. And then you say, 'everybody is writing about this charge'. It's a tool of an authoritarian," Ms Pelosi said.

Reuters/AP