WASHINGTON — Following accusations of fraud in Colorado’s U.S. Senate race, Denver District Attorney Mitch Morrissey has asked to review the signatures that Republican candidate Jon Keyser submitted to state officials in order to qualify for the June 28 primary.

An aide to Morrissey confirmed the review, but cautioned the move was a preliminary reaction to allegations that at least 10 signatures that Keyser used to make the ballot were forged by a worker contracted by the campaign.

“As is the practice of our office, specifically the Economic Crime Unit, they review the original complaint and any accompanying documents to determine if there was a crime committed, whether the suspect is identifiable and if we have jurisdiction,” said Lynn Kimbrough, a DA spokeswoman, in a statement.

Kimbrough said the review was sparked by a complaint from the liberal group ProgressNow Colorado, which has targeted Keyser, a former state lawmaker, and his bid to unseat U.S. Sen. Michael Bennet, the Democratic incumbent.

Colorado election rules require that U.S. Senate candidates seeking to make the ballot by petition must gather at least 1,500 valid signatures from each of the state’s seven congressional districts.

Denver7 this week found that 10 signatures collected in District 1 were forged, raising questions about his signature-gathering operation. His campaign cleared the 1,500 mark in District 1 by 20 signatures.

“All signature gatherers sign an affidavit promising they will comply fully with the law including a promise that they personally witnessed every signature on their petition,” said Matt Connelly, Keyser’s spokesman. “That affidavit also says that they are aware of the consequences associated with disobeying the law.”