Multiple U.S. Secret Service agents have been placed on leave following an assassination attempt on former President Donald Trump last month, media outlets reported on Friday.

Fox and CBS reported that at least five Secret Service members involved in the incident, including the head of the Secret Service's Pittsburgh office, had been put on leave.

Security at the July 13 rally in Butler, Pennsylvania, has been under scrutiny, with serious concerns about how the suspect was able to access a nearby rooftop with a direct line of sight to where Republican presidential nominee Trump was speaking.

The Secret Service has said it was "ashamed" of the security lapse and its chief stepped down in the aftermath of the assassination attempt.

Secret Service spokesperson Anthony Guglielmi did not confirm whether the agents were placed on leave but said "we are examining the processes, procedures and factors that led to this operational failure" and "any identified and substantiated violations of policy will be investigated by the Office of Professional Responsibility for potential disciplinary action."

Trump was shot in the ear, a rally attendee was killed and two others were wounded in the shooting. FBI officials have yet to identify a motive for the suspected shooter, 20-year-old Thomas Crooks, who was shot dead by a Secret Service agent after opening fire.

Following the attack, the Secret Service recommended that Trump avoid large outdoor events. Trump subsequently said he would continue outdoor rallies and that the Secret Service had "agreed to substantially step up their operation" to protect him.

Trump spoke from behind a shield of bulletproof glass in North Carolina on Wednesday, his first outdoor rally since the attack.