There are 300 more suspected noncitizens on Colorado's voter rolls, Secretary of State Gessler announced Tuesday in the latest chapter of a contentious national debate over what Republicans say is vulnerability in the voting system.

The latest figures are from the 3,903 people who received letters from Gessler's office questioning their citizenship in August. During a first round of checks, Gessler said 141 others were found to be possible noncitizens based on a federal immigration database.

Critics of Gessler, who is a Republican, have questioned his political motives and argue the checks have the potential to disenfranchise eligible voters. Some of the people who have received letters questioning their citizenship have turned out to be U.S. citizens, and a few of the original 141 have maintained they are citizens.

The majority of the people who are suspected to be noncitizens and on the rolls are unaffiliated voters, which make up more than half, and Democrats, according to data provided by Gessler's office. The proportion in party registration breakdown is similar to the overall number of people who received letters in August.

State election officials did additional checks this month after obtaining immigration identification numbers from the state division of motor vehicles for all of people who received letters. They received letters because at one point they showed proof they weren't U.S. citizens, such as a green card, when obtaining a driver's license.

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The latest figures mean that out of the 3,903 who received letters, 441 are believed to be non-citizens, according to the federal database, which has normally been used to check the status of legal immigrants who receive government benefits.

"It's unacceptable to have ineligible voters casting ballots in our elections," Gessler said. "We want to ensure the most accurate reliable elections possible."

Gessler's office said it has mailed letters to people believed to be ineligible voters, alerting them about the database findings so they can verify their citizenship or voluntarily remove their registrations.

Of the 441 identified as suspected noncitizens, 232 are unaffiliated, 163 are Democrats, and 37 are Republican. Gessler's office has said they did not look at party registration when checking the voter rolls for possible fraud.

Swing states, like Colorado and Florida, have gotten permission from the federal government to use the immigration database to check voter rolls. Others battleground states, like Iowa and Ohio, have also asked for permission to use the database.

Gessler and other Republican election chiefs in those states have come under heavy criticism from Democrats and voter advocacy groups, who question their political motives in a presidential election that polls show will be extremely close.

"It's suspiciously close to the election for someone who has been so partisan for this kind behavior," said Ellen Dumm, a consultant working for voting rights in Colorado.

Dumm said everyone agrees ineligible voters shouldn't cast ballots. But she argued that Gessler should focus on more important issues, like making sure the secretary of state's office website functions properly to allow people to register to vote, and coordinating with clerks on election issues before November. She said the 441 figure amounts to a "rounding error" in the greater scheme, considering there are 3.5 million registered voters in Colorado.

Gessler has forwarded the names of the suspected noncitizens, 441 in all, to county clerks for any potential challenge at the polls if they show up to cast ballots.

"Though the timing is not ideal, I felt it was important to alert these voters that the federal government says they're not citizens," Gessler said in a written statement. He also sent a letter to U.S. Attorney John Walsh in Denver on Tuesday, letting him know of the figures, telling him that many of the voters believed to be noncitizens would appear on voter rolls across the state.

Walsh announced this month that was appointing a prosecutor to look into any voter fraud in the upcoming election. Gessler said in the letter to Walsh that his office only recently completed the citizenship checks because his office didn't get access to the federal immigration database until August.