President Donald Trump at an interview with Reuters in the Oval Office on February 23. REUTERS/Jonathan Ernst News mogul Christopher Ruddy on Sunday said President Donald Trump was furious over how his staggering claim that President Barack Obama wiretapped his office was playing out.

"I spoke with the president twice yesterday about the wiretap story. I haven't seen him this pissed off in a long time," Ruddy wrote in a column on Sunday for Newsmax, the conservative news site he founded.

"When I mentioned Obama 'denials' about the wiretaps, he shot back: 'This will be investigated, it will all come out. I will be proven right,'" Ruddy added.

Trump claimed in a series of tweets on Saturday, without providing evidence, that Obama ordered the wiretapping of phones in Trump Tower weeks before the 2016 election. The claim appeared to be inspired from a story on Breitbart News, the far-right website that was once run by Steve Bannon, who is now Trump's chief strategist.

The White House doubled down on the wiretapping allegation on Sunday, calling for Congress to investigate the claim as part of its investigation into Russia's meddling in the election.

Numerous US officials have fired back at Trump's allegation. The New York Times reported that FBI Director James Comey on Saturday asked the Justice Department to publicly denounce the claim. And former Director of National Intelligence James Clapper said on NBC that "there was no such wiretap activity" against Trump or his campaign.