Texas's Republican Attorney General Ken Paxton sued Democratic US President Joe Biden's administration on Tuesday, saying the federal government was not providing the help it needed in assessing the citizenship status of some of its registered voters.

The lawsuit filed in the US District Court for the Western District of Texas accuses the Biden administration and specifically the Department of Homeland Security of refusing to help it determine the citizenship status of 450,000 of the 17.9 million registered voters in the state.

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It is already illegal for noncitizens to vote in US federal elections and state and private reviews have turned up very few instances of them doing so. Still, Republican presidential candidate Donald Trump and his allies have argued that large numbers of noncitizens could vote in the Nov 5 election, when he faces Democrat Kamala Harris.

The Department of Homeland Security did not immediately respond to a request for comment.

Trump has falsely claimed that his 2020 loss to Biden resulted from widespread voter fraud.

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Paxton's office said he sent a letter earlier this month asking the US government to verify the citizenship status of people who may be unlawfully registered to vote in Texas by Oct 19. His office said he proceeded with a lawsuit when his request was not answered.

His office said there were nearly half a million voters whose citizenship status has not been verified but acknowledged that the majority of those voters were likely citizens and hence eligible to vote.

"While the majority of the voters on the list are likely citizens who are eligible to vote, Texans have no way of knowing whether or not any of the voters on the list are non-citizens who are ineligible to vote without additional information," his office said.