The director of national intelligence at the time of the US election has denied there was any wire-tapping of Donald Trump or his campaign.
James Clapper also told NBC that he knew of no court order to allow monitoring of Trump Tower in New York.
Mr Trump had accused President Barack Obama of ordering the wire-tap, but offered no evidence.
Mr Trump says an inquiry into alleged Russian interference should also probe potential abuse of executive power.
James Clapper, who left his post when Mr Trump took office on 20 January, told NBC’s Meet the Press: “There was no such wire-tap activity mounted against the president-elect at the time, as a candidate, or against his campaign.”
He said that as intelligence director he would have known about any “court order on something like this. Absolutely, I can deny it.”
Some media reports had suggested the FBI had sought a warrant from the foreign intelligence surveillance court (Fisa) in order to monitor members of the Trump team suspected of irregular contacts with Russian officials.
Mr Clapper’s comments appear to contradict the reports, which said that a warrant was at first turned down, but then approved in October.
Under Fisa, wire-tapping can only be approved if there is probable cause to believe that the target of the surveillance is an agent of a foreign power. Mr Obama could not lawfully have ordered such a warrant.
In his interview, Mr Clapper also said that no evidence had been found of collusion between the Trump team and the Russian government.
Mr Trump, who has faced intense scrutiny over alleged Russian interference in support of his presidential bid, made his wire-tapping allegation in tweets written from his weekend home in Florida early on Saturday.
He called the alleged tapping “Nixon/Watergate”, referring to the notorious political scandal of 1972, which led to the downfall of President Richard Nixon.
His claims sparked Republican and Democrat politicians alike to demand details to back them up. Florida Republican Senator Marco Rubio was the latest, saying on Sunday that “the White House will have to answer as to exactly what he was referring to”.
What are the Congressional committees looking at?
Both the House and Senate intelligence committees are currently looking into the possibility of Russian interference during the 2016 election, both launched in January.
They have promised wide-ranging investigations, carried out on a bipartisan basis, which will not shy away from looking into potential links between the Trump campaign and the Kremlin, as well as Russian “cyber activity”.
Meanwhile, the Senate Armed Services Committee is going to look at how to protect the US from cyber-attacks in the wake of the election.
But in his series of tweets on Sunday, White House Press Secretary Sean Spicerdid not provide any further evidence.
He said: “Reports concerning potentially politically motivated investigations immediately ahead of the 2016 election are very troubling.
“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.”
He added: “Neither the White House nor the President will comment further until such oversight is conducted.”
White House deputy press secretary Sarah Huckabee Sanders told ABC News that if Mr Trump’s allegations were true, “this is the greatest overreach and the greatest abuse of power that I think we’ve ever seen and a huge attack on democracy itself”.
Mr Trump’s tweets followed allegations made by conservative radio host Mark Levin, including that the Obama administration “sought, and eventually obtained, authorisation to eavesdrop” on the Trump campaign last year.
Mr Obama’s spokesman, Kevin Lewis, said the accusation was “simply false”.
A “cardinal rule of the Obama Administration was that no White House official ever interfered with any independent investigation led by the Department of Justice”, he said.
That statement left open the possibility that a judicial investigation had been taking place.
Some Democrats have suggested Mr Trump’s allegations were an attempt to focus attention away from the Russian affair.
House Democratic Leader Nancy Pelosi said: “The Deflector-in-Chief is at it again.”