Election officials in Pennsylvania have found several hundred ballots cast illegally by people who reside in the state but aren't U.S. citizens, dating back to 2000, after previously acknowledging a software glitch that improperly allowed them to register to vote.

The Associated Press reported Wednesday that the Pennsylvania Department of State's Jonathan Marks reported to a state House committee that his office found 544 ballots cast illegally out of 93 million during the past 18 years.

Marks also reportedly cautioned that the number could rise.

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The news comes just weeks after Pennsylvania's top election official, Secretary of the Commonwealth Pedro Cortés (D), resigned without explanation. Cortés said during a 2016 hearing that the glitch in the state's driver licensing software "may inadvertently register" noncitizen immigrants to vote without their knowledge.

A Republican member of the state's election commission in September called the glitch a serious issue, explaining that the improper voter registrations could result in denial of citizenship for the immigrants through no fault of their own.

"This is a real concern," Al Schmidt told The AP. "It is harmful to election integrity, and it is harmful to members of the immigrant community who are applying for citizenship. If you've registered to vote in the U.S., and you're not a citizen, it's potential grounds for the denial of your citizenship application."

About 6.1 million people voted in Pennsylvania during the 2016 presidential election.

President Trump won the state with 48.6 percent of the vote, topping former Secretary of State Hillary Clinton Hillary Diane Rodham ClintonJoe Biden looks to expand election battleground into Trump country Biden leads Trump by 12 points among Catholic voters: poll The Hill's Campaign Report: Biden goes on offense MORE by less than 100,000 votes.

A month after taking office, Trump established a White House commission to investigate his unproven claim that millions of undocumented immigrants voted for Clinton during the election.