A longtime confidante to Hillary Clinton refused to acknowledge Monday whether he has been interviewed by the FBI in the course of its investigation of Clinton's private email server.

Sidney Blumenthal, who served as an informal advisor to Clinton when she was secretary of state, told MSNBC's Chris Matthews he hoped the investigation of Clinton's personal email network would be transparent before refusing to describe the extent of his involvement in it.

"My feeling about this is that I'm as eager as anybody for this to be resolved, and what I would like [is] for this to be completely transparent, and for the Department of Justice to finally issue its report," Blumenthal said during an appearance on the network Monday evening. "I have been urging transparency. I urged that my deposition before the Benghazi Committee be made public the second I walked out. I wanted it to be a public hearing and not a private one."

Blumenthal's interview with the House Select Committee on Benghazi last year was conducted in a closed-door session, as have nearly all of the 98 witness interviews taken by the panel.

The former Clinton aide declined to say whether he had been interviewed by the FBI following reports last week that investigators have already questioned a number of Clinton's closest aides.

"I really don't want to talk about an ongoing inquiry right now," Blumenthal said. "My feeling about it is, that let's wait and see at the end, and see what happens to everybody involved in it, and see what the resolution is, and then I would like to see the Department of Justice issue a very transparent report."