Top law enforcement officials have countered a claim by Democratic Sen. Bill Nelson that Russian operatives had penetrated some county election systems in his home state of Florida.

In a Monday letter obtained by Fox News, Homeland Security Secretary Kirstjen Nielsen and FBI Director Christopher Wray told Florida officials that while Russian spies “have previously demonstrated both the intent and capability to conduct malicious cyber operations,” there is no current evidence to suggest any meddling in the upcoming midterm elections in November.

“DHS and the FBI will continue to notify any victim of a successful cyber intrusion into their election network in any jurisdiction nationwide,” the letter, which was first reported by the Orlando Sentinel, stated.

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The letter is the latest blow to Nelson's claims. It comes after Florida Secretary of State Ken Detzner sent letters to the DHS, FBI and congressional leaders inquiring about the senator's assertions.

Nelson made the unsubstantiated claim earlier this month. He said Russian agents “have already penetrated certain counties in the state and they now have free rein to move about.” He added that voting machines in Florida have already been compromised by Russian meddling.

The senator’s claim drew quick retorts from a number of prominent Republicans, including Florida Gov. Rick Scott who is challenging Nelson for his Senate seat. Scott demanded that the three-term Democratic incumbent provide proof of his claim and raised the concern that Nelson may have revealed classified information.

"Until the essential question is answered – was Nelson revealing classified information or did he make this up – until that answer is clearly marked out by the senator, I think that these questions are not going away," Lauren Schenone, the press secretary for Scott's campaign, told The Hill.

Nelson, and fellow Florida Sen. Marco Rubio, a Republican and a member of the Senate Intelligence Committee, wrote to election officials back in July warning about potential threats to their state’s election apparatus. Nelson and Rubio suggested that 2018 would be a year that demands “greater awareness of cyber threats,” and encouraged state officials to take advantage of the “wide range of services” provided by the FBI and the Department of Homeland Security to safeguard against such intrusion.

Despite the criticism from Scott and other Republicans, Nelson has refused to back down from his comments.

During stops in north Florida over a two-day period last week, Nelson said state and local officials need to take Russian meddling as a "serious threat" and county election supervisors need to make sure they have help to protect their election systems. Russian hackers targeted at least 21 states, including Florida, during the last election.

"It would be foolish to think that the Russians are not continuing to do what they did in Florida in 2016," Nelson said. "It is unfortunate that some Florida officials are trying to use this for partisan purposes."

Fox News' Alex Diaz and The Associated Press contributed to this report.