"How low has President Obama gone to tap my phones during the very sacred election process. This is Nixon/Watergate. Bad (or sick) guy!," Trump said in a series of Tweets on his Twitter account early on Saturday. "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!"
Obama's office did not immediately respond to a request for comment from Reuters. The White House also did not respond to a request to elaborate on Trump's accusations.
Trump is "having meetings, making phone calls and hitting balls" at his golf course in West Palm Beach, according to a Trump spokeswoman.
In one of the Tweets, Trump said the alleged wiretapping took place in his Trump Tower office and apartment building in New York, but there was "nothing found."
Trump's administration has come under pressure from Federal Bureau of Investigation and congressional investigations into contacts between some members of his campaign team and Russian officials during his campaign.
Obama imposed sanctions on Russia and ordered Russian diplomats to leave the United States in December over the country's involvement in hacking political parties in the Nov. 8 US presidential election.
On Saturday, Representative Eric Swalwell, a Democrat who is a member of the House Intelligence Committee, told Fox News that Trump "is not credible when it comes to talking about Russia."
Swalwell downplayed Trump's allegation. "I think this is just the president up early doing his routine tweeting, he said. "Presidents don't wiretap anyone. These are pursued by the Department of Justice in accordance with the FBI and signed off by a judge."
Under US law, a federal court would have to have found probable cause that the target of the surveillance is an "agent of a foreign power" in order to approve a warrant authorizing electronic surveillance of Trump Tower.
Several conservative news outlets and commentators have made similar allegations about Trump being wiretapped during the campaign in recent days, without offering any evidence.
Trump's national security adviser, Michael Flynn, resigned in February after revelations that he had discussed US sanctions on Russia with the Russian ambassador to the United States before Trump took office.
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.
Trump has often used his Twitter account to attack rivals and for years led a campaign alleging that Obama was not born in the United States. He later retracted the allegation.
Barack Obama greets Donald Trump at inauguration ceremonies swearing in Trump as president on the West front of the US Capitol in Washington. January 20, 2017, file picture.
US President Donald Trump on Saturday accused former President Barack Obama of wiretapping him in October during the late stages of the presidential election campaign, but offered no evidence to support the allegation.
