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FBI Director Comey acknowledges it may be "extremely frustrating to some folks" that he cannot say more about the FBI investigation.

"Because it is an open, ongoing investigation and is classified, I cannot say more about what we are doing and whose conduct we are examining," Comey says.

"We just cannot do our work well or fairly if we start talking about it when we're doing it."  

James Comey says the investigations are "very complex" and he "cannot give a timetable on when the work will be done".

FBI Director James Comey confirms publicly for the first time the Bureau is investigating alleged Russian interference in the 2016 presidential election.

The inquiry will include any potential coordination between Trump campaign associates and Russia's government.  

He says: "I have been authorised by the DOJ (Department of Justice) to confirm that the FBI as part of our counter-intelligence mission is investigating the Russian government's efforts to interfere in the 2016 presidential election." 

That includes alleged links between campaign staff and Russian agents, Mr Comey explains.

NSA Director Admiral Mike Rogers says "there is no change in our confidence level on this assessment", referring to the US intelligence community’s report that Russia meddled in the 2016 US elections.

He continues: "It would be difficult to overstate the breadth and scale of malicious cyber activity occurring today."  

"Our adversaries, including nation states, have not rested in trying to penetrate government systems, steal our private industries' intellectual property" and develop cyber-attack capabilities.    

Schiff, the leading Democrat, calls for an independent investigation, similar to the one after the attacks of 11 September 2001.

"The stakes are nothing less than the future of our democracy and liberal democracy, because we are engaged in a new war of ideas. 

"Not communism versus capitalism, but authoritarianism versus democracy and representative government. And in this struggle our adversary sees our political process as a legitimate field of battle."

Adam Schiff cites former British spy Christopher Steele’s allegations of links between former Trump foreign policy adviser Carter Page and Igor Sechin, the US-sanctioned chief of oil giant Rosneft.

Schiff says the committee will identify if Russia had the help of US citizens, including members of the Trump campaign.

Some of Trump's associates, including former campaign manager Paul Manafort, and his former advisers, Roger Stone and Carter Page, have been accused of links with Russian intelligence officials during trips to the country.

But Schiff says they do not know yet if the Russians had the help of US citizens, including those on the Trump campaign.

"We owe it to the country to find out," he says.

Committee chairman Republican Devin Nunes says: "Let me be clear: We know there was not a wiretap on Trump Tower."  

But he adds: "It's still possible that other surveillance activities were used against President Trump and his associates."

Adam Schiff says it is unknowable if Russia's actions had an effect on the election, but that this "does not matter", what mattered was that the "Russians successfully meddled in our democracy". 

Leading Democrat Adam Schiff says Russia's "autocratic ruler" Vladimir Putin may have directed intelligence services as early as 2015 to launch "spear phishing" attacks against US government computers.

They later "weaponised" the stolen data to embarrass Hillary Clinton, who Putin "despised", Schiff says.

"The fact that Russia hacked US election-related databases comes as no shock to this committee."

We have been closely monitoring Russian aggression for years," Chairman Devin Nunes says in the first minutes of his opening remarks.  

The California Republican adds that "numerous" current and former US officials have leaked "purportedly classified information" and that his committee aims to identify and bring those officials to justice.

Also today on Capitol Hill, Supreme Court nominee Judge Neil Gorsuch will be giving his first full day of testimony to the Senate Judiciary Committee.

The conservative federal appeals court judge from Colorado is widely expected to do well, and has been praised by both parties. He has several days of testimony to give, before a full vote by the US Senate comes.

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C-Span is streaming the entire House Intelligence Committee hearing  , external on its website.

Watch the all the action there, including testimony from the directors of the FBI and NSA.

Director James Comey of the FBI has just entered the building, and he did not take questions from reporters on his way inside.

Watch here, external (flash required)

Michael McFaul, who served as the US ambassador to Russia under Obama, is live-tweeting his reaction to the congressional inquiry into Russia's alleged influence on the 2016 election.

Hours before testimony was due to begin, the president took to Twitter, asserting again that the whole "Russian story" was "FAKE NEWS".

He's also been accusing his old rivals, the Clintons and the Democratic party, of trying to sabotage the FBI's investigation. 

Gary O'Donoghue
Washington Correspondent

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Just over two weeks ago, President Trump made an explosive allegation about his predecessor on social media - that President Obama had ordered a wiretapping of the Trump campaign before the election.

And since then the administration has continued to repeat the claims. 

The idea that Britain's GCHQ intelligence agency was asked to perform the wiretap - floated by the president's press secretary -  has drawn a public rebuke from Downing Street and from the intelligence services, who called it nonsense. 

Today the head of the FBI, James Comey, will be asked by the House Intelligence Committee whether there's any validity to the claim, and most expect him to say no. 

But while that might be embarrassing for the White House, the administration is more likely to focus on anything Mr Comey says about alleged collusion between the Trump campaign and Russia during the election.

If he says, as others have, there is no evidence of collusion, that will help Mr Trump bat away a more damaging set of allegations - namely that he was too close to a hostile foreign power.

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After months of closed-door debate, the issue of whether Russia sought to influence the 2016 US presidential election in favour of Donald Trump moves into the open. FBI Director James Comey has given several classified briefings to lawmakers in recent weeks, but today he will be asked by them to publicly comment on any connections the Trump campaign had with the Russian government.

Republican Congressman Devin Nunes, who is leading the House Intelligence Committee inquiry, said this hearing means that “for the first time the American people, and all the political parties now, are paying attention to the threat that Russia poses”.

Despite testimony from the directors of the FBI and NSA, the American people are still likely to have lingering questions after today’s session, since much of the information is classified Top Secret, and therefore won’t be publicly discussed.

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