President Donald Trump has been urged to provide evidence to back his allegation that former President Barack Obama ordered his phones to be tapped during the election campaign.

Republican Senator Ben Sasse said the president’s comments were “serious” and he should explain the alleged wiretapping and how he came to know about it.

Donald Trump has supplied no details to back his claim.

Yesterday, Barack Obama’s spokesman, Kevin Lewis, said the former president had never ordered surveillance of any US citizen.

Donald Trump’s tweets follow allegations made by conservative radio host Mark Levin, including that the Obama administration “sought, and eventually obtained, authorization to eavesdrop” on the Trump campaign last year.

Other media reports had previously suggested the FBI had sought a warrant from the foreign intelligence surveillance court (FISA) in order to monitor members of the Trump team suspected of irregular contacts with Russian officials.

The warrant was first turned down but then reportedly approved in October 2016, though there has been no official confirmation.

Under FISA, wiretapping can only be approved if there is probable cause to believe that the target of the surveillance is an agent of a foreign power. President Barack Obama could not lawfully have ordered such a warrant.

Donald Trump, who has been facing intense scrutiny over alleged Russian interference in support of his election campaign, made the allegation in a series of tweets on March 4.

Writing from his weekend home in Florida, Donald Trump called the alleged tapping “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.

Kevin Lewis said the accusation was “simply false”.

He said that 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 had been taking place.

Earlier Ben Rhodes, who was Barack Obama’s foreign policy adviser and speechwriter, also addressed Donald Trump’s claims in a tweet, saying: “No President can order a wire-tap. Those restrictions were put in place to protect citizens from people like you.”