There are "no indications" that Trump Tower was under surveillance by the US government before or after the election, a Senate committee has said.
The statement from Republican Senator Richard Burr, Senate Intelligence Committee chairman, dismissed Donald Trump's claim his phones were tapped.
Mr Trump had accused his predecessor Barack Obama of wiretapping Trump Tower during the presidential race.
But White House spokesman Sean Spicer said Mr Trump maintains his claims.
"He stands by it," Mr Spicer said at a daily news briefing on Thursday.
The press secretary refused to accept the Senate Intelligence Committee report, saying "they're not findings".
Mr Spicer quoted at length from an unproven Fox News report suggesting Mr Obama had dodged US restrictions by asking Britain's GCHQ electronic surveillance agency to monitor Mr Trump, an allegation already dismissed as "utterly ridiculous" by the Cheltenham-based complex.
Mr Burr joins a cadre of Republican lawmakers who have rejected the allegation.
"Based on the information available to us, we see no indications that Trump Tower was the subject of surveillance by any element of the United States government either before or after Election Day 2016" Mr Burr said in a joint statement with Senator Mark Warner, the committee's vice-chairman.
Earlier on Thursday, House Speaker Paul Ryan also said "no such wiretap existed".
Republican chairman of the House intelligence committee Devin Nunes said on Wednesday he doesn't believe "there was an actual tap of Trump Tower".
But that has not deterred Mr Trump, who on Wednesday told Fox News a "wiretap covers a lot of different things".
He also hinted that more details about the alleged surveillance could be revealed in the coming weeks.
"Wiretap covers a lot of different things. I think you're going to find some very interesting items coming to the forefront over the next two weeks," he said in an interview broadcast on Wednesday night.
No evidence of wiretapping, according to:
Mr Trump echoed comments from White House Press Secretary Sean Spicer, who said the president used the word "wiretap" in quotes to broadly refer to "surveillance and other activities".
The White House has yet to provide any evidence of the president's claims, and instead has asked Congress to examine the allegation as part of a wider investigation into alleged Russian interference in last year's election.