Florida's Republican governor is demanding Democratic Sen. Bill Nelson provide proof to back up his claim Russians penetrated the state's voter registration systems.

Gov. Rick Scott, while campaigning Friday in Tampa, questioned how Nelson knew about potential Russian interference. The Florida Department of State and federal agencies have publicly said they don't have evidence to support the claims.

"No one seems to know what Nelson is talking about," Scott said. "This cannot be swept under the rug. Nelson must come clean and provide a thorough explanation. Elections are not something to scare people about."

Read More: Florida secretary of state urges senator to share info on election security

A bipartisan letter signed by both Nelson and Republican Sen. Marco Rubio stated the Russian government had targeted Florida's election infrastructure during the 2016 election. It added that because Homeland Security depends on localities self-reporting suspicious activity, it is possible that more interference occurred and hadn't yet been uncovered. It did not say if any interference attempts were still happening.

Related: Letter supports Sen. Nelson's claims Russians penetrated Florida voter registration

Nelson has not elaborated on comments suggesting Russian agents have "free rein" to move about certain counties' election systems -- saying the details are "classified."

"If Nelson does have classified information, why is he releasing statements to reporters while campaigning and only releasing pieces of this like a game of Clue?" Gov. Scott asked Friday.

Florida elections officials say if the Russians do have the ability to access voting systems, they hope the Homeland Security officials would tell them about it -- something they say hasn't happened.

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