Secretary of State Donetta Davidson says Salazar's office first heard of the alleged problems two months ago, when discrepancies arose after voter registration drives.
Republican and Democratic state party officials say they're unaware of the investigation.
The allegations are one of several problems Davidson is dealing with leading up to next week's primary election.
Clerks in Arapahoe, Denver, Adams and Jefferson counties have also raised questions about voter registrations with addresses that don't exist, and others with similar signatures.
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