James Clapper, 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.
He told NBC that he knew of no court order to allow monitoring of Trump Tower in New York.
Donald Trump had accused President Barack Obama of ordering the wiretap but offered no evidence.
The White House has asked Congress to examine whether the Obama administration abused its powers.
Meanwhile, the New York Times quoted senior officials as saying that FBI director James Comey had asked the justice department to publicly dismiss President Trump’s allegation this weekend.
However, the DoJ has made no such statement, and the Times said neither it nor the FBI had officially commented.
James Clapper, who left his post when Donald 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”.
However, James Clapper added: “I can’t speak for other authorized entities in the government or a state or local entity.”
Some media reports had suggested a warrant was sought from the foreign intelligence surveillance court (FISA) in order to monitor members of the Trump team suspected of irregular contacts with Russian officials.
James Clapper’s comments appear to contradict the reports, which said that a warrant was at first turned down, but then approved in October 2016.
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. President Obama could not lawfully have ordered such a warrant.
In his interview, James Clapper also said that no evidence had been found of collusion between the Trump team and the Russian government.
Donald 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.
The president called the alleged tapping “Nixon/Watergate”, referring to the notorious political scandal of 1972, which led to the downfall of President Richard Nixon.
Donald Trump’s claims sparked Republican and Democrat politicians alike to demand details to back them up. Florida Republican Senator Marco Rubio was the latest, saying on March 5 that “the White House will have to answer as to exactly what he was referring to”.
However, in his series of tweets on March 5, White House Press Secretary Sean Spicer did not provide any further evidence.
Sean Spicer 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.”
The press secretary 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 President 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”.