Trump asked to retract or substantiate wiretapping claim

Senator John McCain has asked President Donald Trump to either retract or substantiate his claim that his predecessor Barack Obama wire-tapped him in the final weeks of the presidential campaign.

"The State of the Union has no reason to believe Trump's allegation. The President has not supported it with any evidence. I have no reason to believe that the charge is true, but, I also believe that the President of the United States could clear this up in a minute," CNN quoted McCain as saying.

Under the Foreign Intelligence Surveillance Act, law enforcement agencies must obtain a warrant from a secret court to undertake such monitoring

Reports that Trump's associates contacted Russians known to US intelligence during the campaign have dogged Trump for months, raising questions about whether those contacts had anything to do with Russia's meddling in the US election.

The US intelligence community had concluded that Moscow launched an aggressive hacking campaign to undermine the candidacy of Democratic nominee Hillary Clinton.