Mr Trump issued the allegations in a series of early morning tweets on Saturday, but offered no evidence to support the allegation.

"How low has President Obama gone to tapp my phones during the very sacred election process. This is Nixon/Watergate. Bad (or sick) guy!," Mr Trump said.

Mr Obama's office did not immediately respond to a request for comment.

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".

It's the second time inside a week Mr Trump has attacked his predecessor.

In an interview on Fox News on Monday, Mr Trump accused Mr Obama of orchestrating protests again his new administration.

On Saturday, Eric Swalwell, a Democrat who is a member of the House Intelligence Committee, downplayed Mr Trump's allegation.

"I think this is just the president up early doing his routine tweeting," he told Fox News.

"Presidents don't wiretap anyone. These (wire taps) are pursued by the Department of Justice in accordance with the FBI and signed off by a judge."

Some current and former intelligence officials also cast doubt on Mr Trump's latest accusations.

"It's highly unlikely there was a wiretap on the president-elect," said one former senior intelligence official, who requested anonymity to speak candidly, told The Washington Post.

"It seems unthinkable. If that were the case by some chance, that means that a federal judge would have found that there was either probably cause that he had committed a crime or was an agent of a foreign power."

A wiretap cannot be used at a US facility without finding probable cause that the phone lines or internet addresses were being used by agents of a foreign power - or by people spying for or acting on behalf of a foreign government.

"You can't just go around and tap buildings," the official said.

The Trump 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 November 8 presidential election.

Mr 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 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 Obama was not born in the US. He later retracted the allegation.

Reuters, The Washington Post