President Donald Trump has accused Barack Obama of wiretapping his phone a month before he was elected.

The president tweeted on March 4: “Terrible! Just found out that Obama had my “wires tapped” in Trump Tower just before the victory. Nothing found. This is McCarthyism!”

Donald Trump went on to say that a court had earlier denied a wiretap request.

He has given no details to back up the claim – or suggested which court order he was referring to.

Media reports in the past few weeks have suggested the FBI had sought a warrant from the foreign intelligence surveillance court (FISA) last summer in order to monitor members of the Trump team suspected of irregular contacts with Russian officials.

The warrant was first turned down but then approved in October, according to the media reports.

There has been no official confirmation and it is also not clear if this evolved into a full investigation.

There has been no comment yet from former President Barack Obama.

Donald Trump tweeted: “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 the Election.”

The president 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.

Donald Trump also called it McCarthyism – the persecution for US Communists and their allies led by Senator Joe McCarthy in the 1950s.

His tweets followed allegations made by conservative radio host Mark Levin, which were later picked up by Breitbart News, the website founded by Steve Bannon, now Donald Trump’s chief strategist.

Mark Levin said there should be a congressional investigation into what he called Barack Obama’s “police state” tactics in his last months in office to undermine Donald Trump’s campaign.

Breitbart summarizes Mark Levin’s accusations, which say that “the Obama administration sought, and eventually obtained, authorization to eavesdrop on the Trump campaign; continued monitoring the Trump team even when no evidence of wrongdoing was found; then relaxed the NSA (National Security Agency) rules to allow evidence to be shared widely within the government”.