US President Donald Trump stands by wiretap claims

US President Donald Trump stands by his accusation the Obama administration tapped his phones during the 2016 presidential campaign, the White House says, despite three senior lawmakers rejecting the claim.

The Republican and Democratic leaders of the Senate intelligence committee said in a statement on Thursday they saw "no indications" of surveillance at Trump Tower in New York as the president claimed in Twitter posts on March 4.

"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," said Republican chairman Richard Burr and senator Mark Warner, the committee's Democratic vice-chairman.

The top Republican in Congress, House of Representatives Speaker Paul Ryan, on Thursday added his voice to those saying there was no sign of a wiretap.

"The point is, the intelligence committees in their continuing, widening, ongoing investigation of all things Russia, got to the bottom - at least so far - with respect to our intelligence community that - that no such wiretap existed," he said.

But White House spokesman Sean Spicer defended Trump's assertion, citing media reports that have discussed intelligence collection on possible contacts between Trump associates and Russia in the campaign.

"There is no question that there were surveillance techniques used throughout this," Spicer said.

When pressed for evidence, Spicer chastised the media for focusing so much attention on comments disparaging Trump's claim about surveillance.

The Russian government has rejected accusations by US intelligence agencies it worked to influence the election in Trump's favour.

Terrible! Just found out that Obama had my "wires tapped" in Trump Tower just before the victory. Nothing found. This is McCarthyism!

— Donald J. Trump (@realDonaldTrump) March 4, 2017

Trump, a Republican, made his allegation six weeks after he took over the presidency from Democrat Barack Obama, saying Obama wiretapped him late in the campaign but provided no evidence.

"How low has President Obama gone to tapp my phones during the very sacred election process. This is Nixon/Watergate. Bad (or sick) guy!," Trump tweeted.

Obama said through a spokesman it was "simply false".

At least four congressional committees added the accusation in their investigations of possible Russian meddling in the election campaign and Russian ties to Trump and his associates.

On Wednesday, House of Representatives intelligence committee chairman Devin Nunes, a Republican, and top Democrat Adam Schiff said they had seen no evidence Trump Tower was tapped and they would ask FBI director James Comey about the issue during a public hearing on Monday.

Trump appeared to back away from his accusation in a Fox News interview on Wednesday night.

"But 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.

- AAP