Former US president Barack Obama never ordered surveillance on any American citizen, a spokesman has said after current President Donald Trump accused his predecessor of tapping his phones during last year's campaign.
"President Obama nor any White House official ever ordered surveillance on any US citizen," the spokesman said in a one-line statement.
Earlier, Mr Trump launched his most virulent attack yet on his predecessor in a stream of tweets, accusing Mr Obama of tapping his phones but without providing any evidence of the explosive charge.
"I'd bet a good lawyer could make a great case out of the fact that President Obama was tapping my phones in October, just prior to Election!" he wrote on Twitter.
I'd bet a good lawyer could make a great case out of the fact that President Obama was tapping my phones in October, just prior to Election!
— Donald J. Trump (@realDonaldTrump) March 4, 2017
"How low has President Obama gone to tapp (sic) my phones during the very sacred election process. This is Nixon/Watergate. Bad (or sick) guy!" he wrote in another tweet, referring to the political scandal that toppled president Richard Nixon in 1974.
Mr Trump's accusations come as his administration remains mired in controversy over communications between Russian officials and some of his senior aides, including Attorney General Jeff Sessions.
In one of the Tweets, Mr Trump said the alleged wire tapping took place in his Trump Tower skyscraper in New York, but there was "nothing found".
Mr Trump's administration has come under pressure from FBI and congressional investigations into contacts between some members of his campaign team and Russian officials during his campaign.
Mr Obama imposed sanctions on Russia and ordered Russian diplomats to leave the US in December over the country's involvement in hacking political groups in the 8 November US presidential election.
Mr Trump's national security adviser, Michael Flynn, resigned in February after revelations that he had discussed US sanctions with the Russian ambassador to the United States before Mr Trump took office.
Mr Flynn had promised Vice President Mike Pence he had not discussed US sanctions with the Russians, but transcripts of intercepted communications, described by US officials, showed that the subject had come up in conversations between him and the Russian ambassador.
Mr Trump has often used his Twitter account to attack rivals and for years led a campaign alleging that Mr Obama was not born in the US. He later retracted the allegation.
