President Donald Trump's accusation that his predecessor ordered his phones to be tapped is "simply false", Barack Obama's spokesman has said.
Kevin Lewis said that "neither President Obama nor any White House official ever ordered surveillance on any US citizen".
Mr Trump had tweeted: "Terrible! Just found out Obama had my "wires tapped" in Trump Tower just before the victory. Nothing found. This is McCarthyism!"
He gave no details to back the claim.
In his statement, Mr Lewis said 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".
The statement left open the possibility that a judicial investigation was taking place.
Earlier Ben Rhodes, who was Mr Obama's foreign policy adviser and speechwriter, also addressed Mr Trump's claims in a tweet, saying: "No President can order a wiretap. Those restrictions were put in place to protect citizens from people like you."
Mr Trump, who is at his Florida resort, fired off a series of tweets from just after 06:30 local time (11:30 GMT) on Saturday.
He called the alleged tapping "a new low" and said "This is Nixon/Watergate" - referring to the most notorious political scandal of 1972, which led to the downfall of President Richard Nixon after a web of political spying, sabotage and bribery was exposed by the media.
McCarthyism, which Mr Trump referred to in one of the first posts, relates to the persecution of US Communists and their allies led by Senator Joe McCarthy in the 1950s.
In other developments on Saturday:
ABC News quoted senior White House sources as saying President Trump had gone "ballistic" at an Oval Office meeting on Friday, in particular at the decision of Attorney General Jeff Sessions to remove himself from an investigation into alleged Russian interference in the election
Politico and CNN report that Mr Trump will sign as early as Monday a new executive order imposing a travel ban on people from some Muslim-majority nations. The first was halted in the courts
Trump supporters have held scores of rallies in locations across the country, ranging from several dozen people to the low hundreds, under the banner of the Spirit of America
Credit: BBC