An irritated district attorney said he has some concerns about the sincerity of Sheriff Ross Mirkarimi's guilty plea to a misdemeanor charge of false imprisonment in a domestic violence case.

Statements Mirkarimi made in the days after he entered his plea Monday is leading District Attorney George Gascon to question whether the sheriff believes he is guilty of any crime, Gascon told the San Francisco Chronicle editorial board Thursday.

"There is a guilty plea here, and I know there's almost an attempt to deny that this has occurred: I didn't really do this. I'm being forced to do this. That's very concerning to me, to be very honest with you," Gascon told the newspaper.

Gascon said he plans to take up the issue with the judge during Mirkarimi's sentencing on Monday.

Under a plea agreement, Mirkarimi could be fined $590 and sentenced to three years of probation along with counseling, community service and mandatory domestic violence treatment classes.

Mirkarimi's attorney Lidia Stiglich said her client unconditionally accepted responsibility for the incident.

"There is no dispute here, and I would not like to create one," she said in a text response to the newspaper. "RM pled guilty to the charge."

Mirkarimi was accused of bruising the arm of his wife, Venezuelan actress Eliana Lopez, during an argument in front of their toddler son at their San Francisco home on New Year's Eve.

Prosecutors agreed to drop more serious charges, including domestic violence battery, child endangerment and dissuading a witness, in exchange for his plea to false imprisonment.

Later, Mirkarimi told reporters his mounting legal bills -- $125,000 and counting -- along with intense media coverage had been taking a toll on his family and was a considerable factor to take the plea deal.

That led Gascon to wonder about Mirkarimi's motive.

"Either he was lying to the court when he said he was guilty or he's lying now," Gascon said. "There's really no two ways to look at it."