A Georgia district attorney investigating former President Donald Trump for possible meddling in the 2020 election has asked the FBI to provide extra security for her office in the wake of Mr. Trump criticizing prosecutors and suggesting he would pardon people involved in the Jan. 6, 2021, riot at the U.S. Capitol.

Fulton County District Attorney Fani Willis told the FBI in a letter that “security concerns were escalated [last] weekend by the rhetoric of former President Trump … Mr. Trump made multiple references to investigations … including the criminal investigation underway in my office.”

She asked that the FBI conduct “an immediate risk assessment” of the Fulton County Courthouse and provide resources, including “intelligence,” and agents.

At a rally in Texas on Saturday night, Mr. Trump said if he runs for president in 2024 and wins, he will treat the Jan. 6 defendants “fairly.”

“And if it requires pardons, we will give them pardons because they are being treated so unfairly,” Mr. Trump said.

People in the pro-Trump mob at the Capitol were attempting to stop Congress from certifying the Electoral College results that showed President Biden won the election.

Ms. Willis also cited comments from Mr. Trump that she said were directed at her investigation.

“If these radical, vicious, racist prosecutors do anything wrong or illegal, I hope we are going to have in this country the biggest protests we have ever had in Washington, D.C., in New York, in Atlanta and elsewhere, because our country and our elections are corrupt,” Mr. Trump said.

The former president told the crowd that the prosecutors investigating him are “mentally sick” and that their real goal is to harm his supporters.

“In reality, they’re not after me, they’re after you, and I just happen to be the person that’s in the way,” Mr. Trump said.