TAMPA — Russian operatives have "penetrated" some of Florida's voter registration systems ahead of the 2018 midterms, U.S. Sen. Bill Nelson said Wednesday, adding new urgency to concerns about hacking.

The state, however, said it has received "zero information" supporting his claim.

"They have already penetrated certain counties in the state and they now have free rein to move about," Nelson told the Tampa Bay Times before a campaign event in Tampa. He said something similar a day earlier in Tallahassee but declined to elaborate.

"That's classified," the Democrat said Tuesday.

He is facing a re-election challenge in November from Gov. Rick Scott, whose administration said it has no knowledge of the allegations made by Nelson.

PREVIOUS COVERAGE: Florida elections supervisors urged to take federal help on security

Nelson and Florida's other senator, Republican Marco Rubio, wrote a July 2 letter to the 67 county election supervisors about potential threats. But that letter lacked the specificity Nelson laid out.

"County election boards should not be expected to stand alone against a hostile foreign government," the lawmakers wrote in recommending "a wide range of services" from the Department of Homeland Security.

"We were requested by the chairman and vice chairman of the Intelligence Committee to let the supervisors of election in Florida know that the Russians are in their records," Nelson told the Times on Wednesday. (audio below) He noted he is a member of the Armed Services subcommittee on cybersecurity.

"The Florida Department of State has received zero information from Senator Nelson or his staff that support his claims," agency spokeswoman Sarah Revell said in a statement. "Additionally, the Department has received no information from the U.S. Department of Homeland Security, the Federal Bureau of Investigation or the Florida Department of Law Enforcement that corroborates Senator Nelson's statement and we have no evidence to support these claims.

"If Senator Nelson has specific information about threats to our elections, he should share it with election officials in Florida."

A spokeswoman for U.S. Sen. Richard Burr, R-N.C., chairman of the Intelligence Committee, declined to comment. U.S. Sen. Mark Warner, D-Va., the vice chairman, said in a statement that "Russian activities continue to pose a threat to the security of our elections, as Senators Nelson and Rubio rightly pointed out in their letter. … I hope all state and local elections officials, including Florida's, will take this issue seriously."

The warning comes amid a growing focus on election security ahead of the midterm elections. A July 13 indictment of 12 Russian intelligence officers stated that operatives in November 2016 faked a real election vendor email account to send more than 100 "spearphishing" emails to organizations and personnel involved in administering elections in numerous Florida counties. The email contained malware designed to gain access to computer systems.

Nelson took things farther on Wednesday. His account was partly corroborated by two county officials, who said they heard a similar warning at a private meeting with Rubio in May.

All 67 counties have spent considerable time addressing election security and are in the process of spending federal money to fortify systems, following a 2016 attempt by Russians to hack Florida's elections apparatus.

Nelson's remarks immediately caused a major stir among county elections officials, who are testing equipment, training poll workers and counting mail ballots in advance of the Aug. 28 primary. Pinellas County elections officials immediately contacted the FBI, Homeland Security and other state and federal agencies in a futile attempt to find out more about Nelson's assertion.

"Our office has not seen any indication that we have had any penetration by any bad actions," said Pinellas election's office spokesman Dustin Chase.

PREVIOUS COVERAGE: Rubio's red alert: Florida election officials 'overconfident' about security threat

Rubio, a member of the Intelligence Committee, has raised alarms himself, and continues to express concern, though not as explicitly. Like Rubio, Nelson outlined a scenario in which hackers could alter voter registration records.

"This is no fooling time and that's why two senators, bipartisan, reached out to the election apparatus of Florida to let them know the Russians are in your records and all they have to do, if those election records are not protected, is to go in and start eliminating registered voters," Nelson said Wednesday.

"You can imagine the chaos that would occur on Election Day when the voters get to the polls and they say, 'I'm sorry Mr. Smith, I'm sorry Mr. Jones, you're not registered.' That's exactly what the Russians want to do. They want to sow chaos in our democratic institutions."

PREVIOUS COVERAGE: Rubio meets with Florida election officials over Russia threat

Hillsborough Supervisor of Elections Craig Latimer said Rubio made a similar reference to Russian intrusion during a meeting with election supervisors at the Orlando airport on May 30.

That private meeting was the result of Rubio's stated concerns that county election offices were not taking cybersecurity threats seriously enough, a claim the counties have strongly rejected.

Latimer said about eight or 10 elections officials were in the room. Rubio was asked which counties were targeted. "He looked around the room and said, 'I don't believe it's anybody here,'" Latimer said.

The supervisors at the Orlando meeting said Rubio told them to not discuss details with the news media, and none did, until Nelson's remarks surfaced Wednesday.

Okaloosa Supervisor of Elections Paul Lux, the president of a statewide election supervisors' group, confirmed Rubio's account but described it as so vague that it was of no value in improving election preparations against threats.

"There has been no current communication with anyone about any breach or problem," said Lux, who began polling fellow supervisors to see if any had heard directly from Nelson. Lux said none had.

This post has been updated.

Contact Alex Leary at aleary@tampabay.com. Follow @learyreports. Contact Steve Bousquet at sbousquet@tampabay.com. Follow @stevebousquet. Contact Kirby Wilson at kwilson@tampabay.com. Follow @KirbyWTweets.

Audio: Times staff writer Kirby Wilson interviews Nelson in Tampa.