Several people have been injured when a man set people on fire in the vicinity of a demonstration in the US state of Colorado held to raise awareness on hostages being held in Gaza, said local authorities.

Boulder Police Chief Stephen Redfearn told reporters on Sunday that several individuals sustained injuries, including burns and other wounds. He did not provide an exact number of those injured.

Redfearn said the suspect was " taken into custody without incident" and was transported to a hospital with minor injuries. The suspect's name has not yet been released as the investigation is ongoing.

Local authorities said at least six were injured in the attack, aged 67 to 88.

Boulder Police Department said they were not calling it a terror attack at this time, and it's irresponsible to speculate the motive right now.

However, FBI Director Kash Patel said on X that federal authorities are treating the incident as a "targeted terror attack."

"We are aware of and fully investigating a targeted terror attack in Boulder, Colorado," Patel wrote. "Our agents and local law enforcement are on the scene already, and we will share updates as more information becomes available."

'Investigative tips'

FBI Deputy Director Dan Bongino confirmed the investigation is being pursued as an act of terror and targeted violence.

"All of the necessary assets will be dedicated to this investigation," Bongino said on social media.

"If you have any investigative tips, please contact the FBI. And if you aided or abetted this attack, we will find you. You cannot hide."