America's former top intelligence officer flatly denies Trump's claim Obama had him wiretapped

'There was no such wiretap activity mounted against the president-elect at the time, or as a candidate or against his campaign'

Barack Obama did not wiretap Donald Trump during the 2016 presidential election, according to the United States' previous top intelligence official.

Former Director of National Intelligence James Clapper spoke out as the White House urged Congress to investigate allegations made on Twitter by Mr Trump.

"There was no such wiretap activity mounted against the president-elect at the time, or as a candidate or against his campaign," Mr Clapper told NBC.

For any wiretap to be legal under US law, a federal court has to find "probable cause" that the target is an "agent of a foreign power". Asked if a federal court had issued such an order, Mr Clapper said: "I deny it".

He said he would "certainly hope" to be aware of any wiretap, but added: "I can't speak for other authorized entities in the government or a state or local entity."

But Mr Clapper has previously been accused of lying to Congress about the National Security Agency's surveillance of millions of Americans, as Trump supporters were quick to point out.

Early on Saturday morning, Mr Trump called Mr Obama a "bad, or sick, guy" and accused the then-President of wiretapping his New York office in 2016.

"Terrible!" the President tweeted. "Just found out that Obama had my 'wires tapped' in Trump Tower just before the victory. Nothing found. This is McCarthyism!"

He added: "Is it legal for a sitting President to be 'wire tapping' a race for president prior to an election? Turned down by court earlier. A new low!"

The allegations were denied by Mr Obama's team, while FBI Director James Comey has reportedly called on the Justice Department to publicly refute the claim.

But the Justice Department has yet to issue a formal statement, while Mr Trump's Press Secretary Sean Spicer has doubled down on the accusation.

"President Trump is requesting that as part of their investigation into Russian activity, the congressional intelligence committees... exercise their oversight authority to determine whether executive branch investigative powers were abused in 2016," he said a statement similarly issued through Twitter.

Mr Spicer also described the alleged wiretap as "politically motivated".

President Trump's pick to take over the top intelligence role from Mr Clapper is former Senator Dan Coats, who has described re-authorising the government to spy on internet users' activity as his "top priority".