On Thursday, spokesman Sean Spicer defended the president's comments by repeating a Fox News analyst's report that GCHQ, the British electronic intelligence agency, had helped Mr Obama wiretap Mr Trump.
Spicer pointed specifically to a March 14 broadcast on Fox News, in which analyst Judge Andrew Napolitano said that three sources told the network that Obama went around USA intelligence by having British spies in the Government Communications Headquarters surveil the candidate's conversations.
The Justice Department declined to comment on the contents of the report, but, earlier in the day, a spokeswoman confirmed it had delivered the document.
"Mr. Spicer and Gen. McMaster explained that Mr. Spicer was simply pointing to public reports, not endorsing any specific story", one official said.
The chairs and vice-chairs of both the House and Senate intelligence committees have said there is no evidence of surveillance on Trump Tower.
Both Spicer and National Security Adviser H.R. McMaster reportedly spoke to British officials and vowed that the unsubstantiated allegation would "not be repeated".
The bipartisan leaders of the Senate Intelligence Committee have also stated that no surveillance of Trump Tower occurred during or after the 2016 election.
President Trump recently accused former President Obama of wiretapping Trump Tower during the 2016 presidential campaign. Hurd replied, "I'm going to quote my father, Bob Hurd, and something that he's told all of my friends when they got married - it never hurts to say you're sorry".
"As far as wiretapping I guess by this past administration, at least we have something in common, perhaps", Trump said, turning to Merkel, who did not smile at the joke.
Previously, GCHQ had also dismissed the claim as "utterly ridiculous". "The president's statements before, and his tweets since leading right up today, have no basis in fact", Schiff said.
"I think that was something two days ago that was reported on air.no, no, it has not been raised".
Spicer said, quoting Napolitano, the justification was: "There's no American fingerprints on this".
Trump on Friday repeated his claim against Obama, rejecting rising calls from Republicans and Democrats to withdraw the charge and apologize. But Trump offered no evidence to back up the accusation.
Earlier this week, House Intelligence Committee leaders requested a list of names of any individuals whose names were "unmasked" in the course of surveillance activities focused elsewhere.
Napolitano said that GCHQ had assisted the US National Security Agency (NSA) is the wiretap and that it had been done on the orders of the Obama administration.