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TALLAHASSEE (CBSMiami/AP) — U.S. Senator Bill Nelson is standing by his claims that Russian operatives have penetrated some of his state’s election systems ahead of this year’s election.

Ahead of the 2016 election, Russian hackers targeted at least 21 states, including Florida. An indictment released last month said Russian operatives sent over 100 fake emails to elections offices and personnel in Florida as part of the hacking effort.

Nelson said last week that Russians were able to get inside the election systems of “certain counties” and “now have free rein to move about.” He added that “the threat is real and elections officials — at all levels — need to address the vulnerabilities.”

On Monday, he said that it would be “foolish to think” the Russians are not continuing their efforts to target Florida.

Gov. Rick Scott, who is challenging Nelson is this year’s election, has demanded that the senator provide proof of his claims.

Nelson said criticism of his comments is for “partisan political purposes.”

Last Friday two Republicans who are on the Senate intelligence committee declined to confirm or deny Nelson’s statements.

(© Copyright 2018 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)