Former Whitewater independent counsel and Fox News contributor Ken Starr told "Your World with Neil Cavuto" Thursday that the recently disclosed list of top Obama administration officials who requested the "unmasking" of Lt. Gen. Michael Flynn raises "very serious questions."

"It is so odd that you had so many people and at increasingly high levels [request the unmasking]," Starr told host Neil Cavuto. "It raises a lot of, I think, very serious questions. We don't have the answers to them, but it is a very good reason to be suspicious."

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Earlier Thursday, President Trump pressed Senate Judiciary Committee Chairman Lindsey Graham, R-S.C., via Twitter to call former President Barack Obama to testify. On Wednesday, Sens. Chuck Grassley, R-Iowa, and Ron Johnson, R-Wis., made the list of names public.

Cavuto asked Starr about the possibility that the Judiciary Committee would call Obama as a witness.

"It's all too soon to tell but certainly it is in the realm of possibility, bordering on likelihood, because there was this huge flurry of interest in this [Russian ambassador Sergery] Kislyak communication with an American," Starr said.

Starr told Cavuto that one of the questions that needs to be answered is why personnel not affiliated with the intelligence community were on the list.

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"It is odd to me that so many people were trying to find out through their own resources as opposed to allowing the intelligence community, the appropriate people to say... to piece all these things together, 'We in the intelligence community need an unmasking,'" he said.

"But why did the chief of staff to the president of the United States need to unmask? Why did Vice President Biden need to unmask? There's been no explanation for that."

Fox News' Brooke Singman contributed to this report.