Florida Gov. Rick Scott (R) speaks to Cuban American supporters at a campaign stop in Hialeah, Fla., on July 13. (Wilfredo Lee/AP)

Florida Gov. Rick Scott (R) demanded Friday that Sen. Bill Nelson (D-Fla.) provide evidence to back up his claim this week that Russian operatives have penetrated the election systems of several counties in the state and “now have free rein to move about.”

Scott, who is vying to unseat Nelson in November, addressed the “very serious charge” after an event Friday morning focused on his plans for Latin American policy at Casa Cuba of Tampa, a center for the exile community in Florida.

“Either Bill Nelson knows of crucial information that the federal government is withholding from Florida election officials or is simply making things up,” Scott said.

He called on Nelson to “come clean” and warned, “Elections are not something to scare people about.”

In a statement, Nelson did not address specifics but maintained that he and other lawmakers are working to keep state officials informed.

“I and several of my Senate colleagues are trying to make sure Florida officials are aware of the ongoing Russian threat so they take the steps necessary to safeguard our elections,” he said.

Nelson also took a veiled swipe at Scott, saying that it was “unfortunate that some Florida officials would try to use this issue for personal, political gain.”

On Wednesday, Nelson told the Tampa Bay Times that Russian operatives “have already penetrated certain counties in the state and they now have free rein to move about.”

He declined to provide details. A day earlier, Nelson had responded to questions about the matter by saying the information was classified, the newspaper reported.

The spat is playing out amid an increasingly heated national debate over Russian interference in U.S. elections. In a show of force in the White House briefing room last week, President Trump’s top national security officials warned of continued Russian attempts at interference and vowed that the administration is “doing everything we can” to combat them.

Yet Trump himself has sent contradictory messages on the issue: In late July, he tweeted that Russian interference in the 2016 election, which the U.S. intelligence community has concluded took place, was “all a big hoax.”

The dust-up between Scott and Nelson appears to be the first instance of alleged Russian interference being used as a partisan issue in a highly-contested campaign.

After Nelson’s comments earlier this week, Florida Secretary of State Ken Detzner (R), who was appointed by Scott, sent a letter to Senate Intelligence Committee Chairman Richard Burr (R-N.C.) requesting details on the alleged hacking. Nelson had previously said the committee had been the source of his information.

In the letter, Detzner said that his office had been in touch with federal and state officials, including the Department of Homeland Security and the FBI, but that they had been unable to provide him with further information.

Burr replied in a letter Friday encouraging Detzner to address his questions to federal agencies rather than to his committee. He also voiced support for a letter sent by Nelson and Sen. Marco Rubio (R-Fla.) last month to Florida state and local officials, including Detzner, urging greater cooperation with DHS on the issue.

“The Federal Government has resources to help, and only by working together can we thwart Russia’s continued efforts to interfere in our democracy and undermine our elections,” Burr wrote Friday. “That is also the message of the letter sent by senators Rubio and Nelson, and I support their effort.”

While Nelson’s latest comments on the issue have drawn attention, they echo part of the letter that both he and Rubio sent last month. In that missive, the lawmakers alerted Florida officials to the Senate Intelligence Committee’s finding that “in a small number of cases, cyber actors affiliated with the Russian government accessed voter registration databases” in the state.

In a meeting with nearly a dozen local election officials in May, Rubio also voiced concerns echoing Nelson’s, according to St. Petersburg-based TV station WTSP.

“He made a very similar statement that there was some, it wasn’t in everybody’s system — there was some activity in some systems,” one local supervisor of elections told the station, adding that Rubio had told the assembled officials not to discuss the matter publicly.

Sonmez reported from Washington.