Comey was fired by President Donald Trump early last month as the FBI's own Russia probe increasingly focused on possible collusion between Trump's campaign and a Russian bid to tilt the election in his favor.
Comey is expected to be questioned about the circumstances of his firing and allegations that Trump has tried to stifle the agency's investigation and divert attention to intelligence leaks that have hurt his administration.
His hotly awaited appearance on Capitol Hill comes as probes by the Justice Department and several Congressional committees have moved toward Trump's inner circle, with investigators said to be examining contacts between top White House advisor and Trump son-in-law Jared Kushner and Russian ambassador Sergey Kislyak.
Last week, The Washington Post reported that Kushner made a pre-inauguration proposal to the Russian envoy to set up a secret, bug-proof link with the Kremlin to discuss bilateral relations and other issues like the Syria conflict.
Besides Kushner, other Trump aides and advisors are also in the spotlight.
On Wednesday, the House Intelligence Committee issued subpoenas for Trump's personal lawyer Michael Cohen and his former national security advisor Michael Flynn -- who was also allegedly part of the discussions between Kushner and Kislyak.
The Senate panel hearing is expected to quiz Comey on memorandums he allegedly wrote on three conversations he had with Trump in January and February.
The memorandums -- the contents of which have been leaked to the media and have not been denied by Comey -- reportedly document the president's efforts to get the FBI to ease the investigation's focus on Flynn.
Comey's testimony will come after a new independent special counsel, former FBI director Robert Mueller, was appointed to take over the Justice Department and FBI Russia investigations.
Mueller was chosen to lead the department's investigation on May 17 amid concern of political interference.
Mueller, respected for his independence and thoroughness, has so far been silent about taking over the investigations.
He reportedly has met with Comey to discuss the probe, and Comey reportedly sought his approval to testify.
Attorney general pressed on Russia ties
Besides Kushner, Cohen and Flynn, the Justice and Congressional investigations are also looking into the Russia ties of former Trump campaign chief Paul Manafort, political consultant Roger Stone, and foreign affairs advisor Carter Page.
Meanwhile on Thursday, two Democratic senators, Patrick Leahy and Al Franken, issued a statement calling the FBI to provide information on alleged meetings that Attorney General Jeff Sessions had with Russian officials last year and that were not reported by Sessions.
"If it is determined that the attorney general still has not been truthful with Congress and the American people about his contacts with Russian officials during the campaign, he needs to resign," they said.
Russian President Vladimir Putin on Thursday again denied state involvement in any US election cyberattacks, but admitted "patriotically minded" hackers might have been involved.
Eyewitness? Submit your stories now via social or:
Email: news@pulselive.co.ke
