Trump-Russia investigation: The 'collusion issue is still open', says Senate intelligence chairman

The committee has also struggled to secure an interview with ex-MI6 officer Christopher Steele, one of the men behind the explosive dossier on Trump

Senate Select Committee on Intelligence Chairman Richard Burr and Vice Chairman Mark Warner update reporters on the status of their inquiry into Russian interference in the 2016 US election (AP)

The Senate intelligence committee is still investigating whether Russia colluded with Trump campaign advisers to influence the 2016 election, the panel's chairman has said.

The “collusion issue is still open”, said Republican Senator Richard Burr, standing alongside the committee's top Democrat, Mark Warner.

The committee is more than nine months into its investigation into Russian meddling in last year’s presidential race.

Mr Burr said the panel has confirmed the findings of US intelligence agencies – that Russia had interfered in the election – but that one portion of the investigation has not yet closed.

The committee has interviewed every intelligence community official involved in drafting the report on Russian election meddling, Mr Burr said, listing off the work the committee has done.

So far, investigators have conducted more than 250 hours of interviews, produced over 4,000 transcript pages and reviewed more than 100,000 pages of documents.

The committee has spoken behind closed doors to multiple current and former members of Donald Trump's inner circle, including the President’s ex-campaign chairman Paul Manafort and son-in-law Jared Kushner.

But despite their efforts, the committee has still not been able to interview Christopher Steele, the author of a controversial dossier containing explosive allegations about Mr Trump and top members of his campaign.

“The committee has hit a wall,” Mr Burr said, adding that both he and Mr Warner made personal efforts to reach Mr Steele, but he had not accepted their invitations.

The Republican said the panel cannot determine the dossier’s credibility without understanding who paid for it and who contributed to the material.

However, the Senate Judiciary Committee – which is also conducting its own Russia probe – was able to interview the man who hired Mr Steele to compile the report, Glenn Simpson, behind closed doors.

After 10 hours of testimony, Mr Simpson, the co-founder of the political research firm Fusion GPS, stressed that he stood by the allegations in the dossier.

Three congressional panels and special counsel Robert Mueller are investigating Russia’s meddling in the election and possible collusion.