WASHINGTON — One man was killed and another injured in what US authorities said Sunday was a “tragic accident” at a Pride parade in Florida where a pickup truck driver unintentionally accelerated, striking pedestrians.

The incident happened at the start of the Wilton Manors Stonewall Pride Parade and festival on Saturday, an LGBTQ celebration in a town near Fort Lauderdale in the southern US state, causing initial confusion whether the accident was part of a deliberate attack.

Fort Lauderdale Police announced Sunday that the 77-year-old driver was a participant in the festivities who had been selected to drive the lead vehicle due to “ailments preventing him from walking during the duration.”

The white pickup had begun to move forward anticipating the start of the parade when it “accelerated unexpectedly, striking two pedestrians” before crashing into the fence of a nearby business, the police said in a statement.

All three men were members of the Fort Lauderdale Gay Men’s Chorus, the police said, adding that the driver was cooperative with authorities.

The two adult men were transported to a medical center where one later died, according to the statement. The other remains hospitalized but is expected to survive.

“Today we know yesterday’s incident was a tragic accident, and not a criminal act directed at anyone, or any group of individuals,” the Walton Manors Police Department said in a separate statement.

Justin Knight, president of the Fort Lauderdale Gay Men’s Chorus, called the incident an “unfortunate accident.”

“Our thoughts and prayers are with those affected by the unfortunate accident that occurred when the Stonewall Pride Parade was just getting started,” he said in a statement Saturday.

Fort Lauderdale Mayor Dean Trantalis, who was at the parade, initially told a local broadcaster he thought the crash was “deliberate.”

In the immediate aftermath, he called it “a terrorist attack against the LGBT community” and claimed the truck had targeted the car of a Democratic congresswoman, Debbie Wasserman Schultz — who was in a convertible waiting to take part in the procession — but narrowly missed her.

Trantalis explained on Sunday that he had initially “feared it could be intentional based on what I saw from mere feet away.”

“As the facts continue to be pieced together, a picture is emerging of an accident,” he said.

Wasserman Schultz said on Twitter that she was “heartbroken” by what had taken place.

“I am deeply shaken and devastated that a life was lost,” she said.

“My staff, volunteers and I are thankfully safe,” she added.

The Wilton Manors Police Department tweeted Saturday night after the crash that the public was not in danger.

June is Pride Month, which commemorates the 1969 Stonewall riots sparked by repeated police raids on a popular gay bar in New York. The demonstrations proved to be a turning point in the LGBTQ community’s struggle for civil rights.