Former FBI Director James Comey said on Thursday he has no doubt that Russia interfered with last year's US presidential election. 

Comey was testifying to the US Senate Intelligence Committee about Moscow's alleged involvement in the vote.

Comey said that the FBI became aware of Russia's cyber intrusion in late summer 2015.

Comey initially said that Trump did not ask him to stop the probe into former national security adviser Michael Flynn before retracting the statement, Reuters reported.

The former FBI director was fired by Trump on May 9.

Democratic Senator Mark Warner said in an opening statement, "This is not how a president of the United States behaves.

"Regardless of the outcome of our investigation into those Russia links, Director Comey's firing and his testimony raise separate and troubling questions that we must get to the bottom," he added.