The Senate Intelligence Committee has asked 20 people to be questioned in its investigation of Russian interference in last year's presidential election.
The panel will hold its first public hearing on Thursday.
"This one is one of the biggest investigations the Hill has seen in my time here," the CNN quoted panel Chairman Richard Burr as saying at a news conference with committee Vice-Chairman Mark Warner.
Burr and Warner said that they have 20 witnesses they plan to interview and have scheduled interviews with five of them so far. The committee leaders said that they are happy that President Donald Trump's son-in-law, Jared Kushner, and former campaign chairman Paul Manafort have agreed to testify, but they have not yet decided when they will bring them in.
"To date, we have made 20 requests for individuals to be interviewed by the committee. As we stand here today, five are already scheduled on the books, and probably within the next 10 days the remaining 15 will have a scheduled date for those individuals to be interviewed by our staff. We anticipate inviting additional individuals to come and be interviewed, and ultimately some of those interviewed individuals may turn into private or public hearings by the committee, but yet to be determined," said Burr.
"It would be safe to say we have had conversations with a lot of people, and it would be safe to say Gen Flynn (Former National Security Adviser Michael Flynn) is a part of that list," he added.