At least eight people were injured in an attack in Boulder on Sunday after an attacker used a makeshift flamethrower and hurled an incendiary device into a crowd calling for the release of Israeli hostages in Gaza.
Authorities said the suspect, identified as 45-year-old Mohamed Sabry Soliman, yelled "Free Palestine" before attacking the crowd in what the FBI is treating as an "act of terrorism".
The victims, aged 52 to 88, were taken to hospitals in the Denver area with injuries ranging from "minor to serious". They are being treated for burns among other injuries, police said.
Soliman was arrested at the scene and taken to the hospital for treatment, but authorities did not elaborate on his injuries.
One video showed him shirtless and holding two clear bottles with transparent liquid in them whilst shouting at onlookers who had assembled in a pedestrianised zone for a peaceful protest for Israeli hostages still held in Gaza.
Another video shows a witness shouting, “He’s right there. He’s throwing Molotov cocktails,” as a police officer with his gun drawn advanced on the suspect.
FBI leaders in Washington said they were treating the attack as an act of terrorism, and the Justice Department — which leads investigations into acts of violence driven by religious, racial or ethnic motivations — decried the attack as a “needless act of violence, which follows recent attacks against Jewish Americans.”

“This act of terror is being investigated as an act of ideologically motivated violence based on the early information, the evidence, and witness accounts. We will speak clearly on these incidents when the facts warrant it,” FBI Deputy Director Dan Bongino said in a post on X.
Authorities believe Soliman intentionally attacked the demonstrators, who are part of a volunteer group called Run for Their Lives, which organises run and walk events to call for the immediate release of the Israeli hostages who remain in Gaza since they were captured by militants during the incursion into southern Israel that started the Israel-Hamas war in 2023.
Prosecutors 'fully united'
The incident in Colorado comes at a time of inflamed tensions in the US over Israel's war in the Gaza Strip, which has sparked an increase in antisemitic violence.
A week earlier, two Israeli Embassy staffers were shot to death in Washington by a man who yelled, "I did it for Palestine" as he was led away by the police.
US President Donald Trump's administration has clamped down on pro-Palestine protests, detaining protesters against the war and cutting off funding to US universities that have permitted such rallies.
Prosecutors said they were "fully united" in ensuring the attacker is held fully accountable. Boulder police said they would step up security ahead of several events celebrating the Jewish holiday of Shavuot scheduled to take place over the next two days.
The Boulder Jewish Community Centre said in a statement, “When events like this enter our own community, we are shaken. Our hope is that we come together for one another.”