FBI Director James Comey confirmed that several investigations looking at Russian meddling in the 2016 election are examining the Trump campaign's contacts with Russian officials. At the same time he quashed President Donald Trump's claims that Obama wiretapped Trump Tower.

Ongoing investigations that are looking at Russia include "investigating the nature of any links between those associated with the Trump campaign," Comey said during testimony before the House Intelligence Committee on Monday 20 March.

He said that he and the Department of Justice "have no information that supports" Trump's tweets – sent on 4 March – that claim he was illegally wiretapped by his presidential predecessor. The statement led Democrat Senate minority leader Sen. Chuck Schumer‏ (D-NY) to call for Trump "to retract his claim immediately."

Comey, whose agents have been investigating, gave testimony about their work alongside National Security Agency director Michael Rogers. He said he was authorised to reveal the existence of the investigation by the Justice Department.

Reports in recent months have revealed leaks that Trump campaign officials are being investigated for their contact with Russian officials in the year leading up to the 2016 election.

At the outset of the hearing, the committee's chair Rep Devin Nunes (R-CA) said that, through its state-backed media outlet RT, Russia has launched an "international disinformation campaign" worthy of old Soviet media mouthpiece Pravda. Ranking committee member Rep Adam Schiff (D-CA) opened the session by repeating Democrat calls for an independent commission.

Comey said he could not reveal any further details about the investigations because the FBI is "very careful about the way we handle information that may be of interest to our foreign adversaries."

"I know that is extremely frustrating to some folks, but it is the way it has to be," he said, adding that while "speculating is part of human nature" no one should take his answers of "no comment" as evidence for anything. Details of other past investigations, he said, have been only given out when those investigations were completed.

"We just cannot do our work well or fairly when we're talking about it while we're doing it," he said, adding that there's no way for him to give a timetable for when the investigations will be completed. "I can promise you we will follow the facts no matter where they lead."

FBI Director James Comey (L) and National Security Agency Director Mike Rogers take their seats at a House Intelligence Committee hearing into alleged Russian meddling in the 2016 U.S. election, on Capitol Hill in Washington, DC 20 March 2017 Reuters/Joshua Roberts