MINNEAPOLIS — A Minnesota prosecutor said Tuesday that he would agree to review allegations of domestic abuse against U.S. Rep. Keith Ellison only if a formal complaint is first investigated by law enforcement.

An ex-girlfriend of Ellison, Karen Monahan, alleged in August that the Democratic congressman dragged her off a bed by her feet and screamed obscenities at her in 2016. On Monday, a draft report by an attorney with links to the state’s Democratic party found that Monahan’s claims were unsubstantiated because Monahan refused to provide video she said she had of the incident.

Ellison, a deputy chairman of the Democratic National Committee, has denied the allegation.

In a letter dated Tuesday, Dakota County Attorney James Backstrom said the Minneapolis city attorney asked him to provide a preliminary review of the matter, citing a conflict of interest because Ellison’s son is on the Minneapolis City Council.

Backstrom told City Attorney Susan Segal that prosecutors generally do not conduct criminal investigations. He said if Monahan, the state’s Democratic-Farmer-Labor Party, or others want to file a complaint alleging criminal conduct, that must be done with law enforcement. Then, it would be up to police to determine how and when to investigate.

“If such an investigation occurs and is submitted to you for review to determine whether or not criminal charges should be filed, I will agree to review the matter on a conflict of interest basis for you,” Backstrom wrote. “However, I will not review any investigation completed by the law firm retained by the Minnesota DFL Party or any other private investigator without the completion of an investigation by a law enforcement agency.”

Monahan’s attorney, Andrew Parker, said Monahan would cooperate with any investigation. He said he hasn’t talked with her about filing a criminal complaint.

“That was not her intention,” Parker said. “Her intention was her healing as an abuse victim … not to get Keith Ellison thrown into jail.”

Ellison is running for Minnesota attorney general. In a statement released Monday, he said he intends to comply with any inquiries.

When asked why Backstrom was asked to review the case, instead of Hennepin County, Segal said the Dakota County Attorney’s Office prosecutes felonies, misdemeanors and gross misdemeanors, while the Hennepin County Attorney’s Office only prosecutes adult felonies. Segal said the types of allegations in this matter don’t appear to rise to the felony level.

Backstrom was first elected Dakota County attorney in 1987 and was listed as nonpartisan on the ballot in 2014.

Ellison was first elected to his Minneapolis congressional district in 2006 and emerged as a leader among liberal Democrats, including co-chairing the Congressional Progressive Caucus. He and Monahan dated for several years but broke up before she accused him of physical abuse.