A top Pennsylvania Republican state senator called Thursday for the resignation of Secretary of the Commonwealth Kathy Boockvar, accusing her of failing to ensure an orderly presidential election in the Keystone State.

Doug Mastriano, chairman of the Senate Intergovernmental Operations Committee, claimed in a lengthy letter to Boockvar that "Pennsylvanians no longer feel secure in casting their vote."

"The nucleus of any free society is confidence that each citizen's vote will count," Mastriano added. "Nothing is more crucial to Americans than confidence that our voices will be heard through voting."

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Mastriano, who has been a vocal opponent of Democratic Gov. Tom Wolf and his administration's ongoing coronavirus restrictions, accused Boockvar of "fail[ing] to deploy even the minimum safeguards."

A retired Army colonel, Mastriano wrote that he had directed NATO's Joint Intelligence Center in Afghanistan, work that included providing "oversight and security to Afghan elections -- a country that had never witnessed an honest election."

Mastriano added that the NATO apparatus helped ensure an election that was both safe and fair, with various security measures in place to ensure one vote per legal voter.

"I wish I could say the same of elections in Pennsylvania during your time as the Secretary of the Commonwealth," he wrote, adding that he and many Pennsylvania voters have "lost confidence" in the secretary's leadership.

On Thursday, Boockvar told reporters that the race between President Trump and Democratic nominee Joe Biden was "very close in Pennsylvania."

"There is no question that means it is going to take longer to actually see the winner,” added Boockvar, who said that “several hundred thousand ballots remain to be counted.”

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“The closer the race is, the longer it takes,” she continued. “The overwhelming majority of ballots will be counted by Friday — we have counted the overwhelming majority, but because it is a close race, it is not quite clear who the winner is.”

The Trump 2020 Campaign has sued Boockvar and boards of elections in each of the state's 67 counties, accusing Democrats of "scheming" to "disenfranchise and dilute" Republican votes.

Fox News' Brooke Singman and Morgan Phillips contributed to this report.