Former President Donald J. Trump was whisked off the stage at his rally in Pennsylvania on Saturday after gunshots were fired toward the area where he was speaking. Officials said the incident was being investigated as an assassination attempt.

The rally took place on the grounds of the Butler Farm Show in Western Pennsylvania, about 35 miles outside of Pittsburgh. In a statement, a spokesman for the Secret Service said that one spectator at the rally was killed and two were critically wounded, and that the Secret Service had killed the suspected shooter.

An AR-15-type semiautomatic rifle was recovered from a deceased white male believed to be the gunman, according to two law enforcement officials. The gunman’s body was seen on a rooftop several hundred feet away from the stage.

“I was shot with a bullet that pierced the upper part of my right ear,” Mr. Trump said in a post on Truth Social, his social media platform. “I knew immediately that something was wrong in that I heard a whizzing sound, shots, and immediately felt the bullet ripping through the skin.” Shortly after the incident, a spokesman for Mr. Trump’s campaign said the former president was “fine” and was being examined at a local medical facility.