Six victims aged between 67 and 88 years old were transported to hospitals, the FBI special agent in charge of the Denver Field Office, Mark Michalek, said. At least one of them was in a critical condition, authorities said.

"As a result of these preliminary facts, it is clear that this is a targeted act of violence and the FBI is investigating this as an act of terrorism," Michalek said.

Michalek named the suspect as Mohamed Soliman, who was hospitalized shortly after the attack. Reuters could not immediately locate contact information for him or his family.

FBI Director Kash Patel also described the incident as a "targeted terror attack," and Colorado Attorney General Phil Weiser said it appeared to be "a hate crime given the group that was targeted." Boulder Police Chief Stephen Redfearn said he did not believe anyone else was involved.

"We're fairly confident we have the lone suspect in custody," he said.

The attack took place on the Pearl Street Mall, a popular pedestrian shopping district in the shadow of the University of Colorado, during an event organized by Run for Their Lives, an organization devoted to drawing attention to the hostages seized in the aftermath of Hamas's 2023 attack on Israel.

In a statement, the group said the walks have been held every week since then for the hostages, "without any violent incidents until today."

The incident comes amid heightened tensions in the United States over Israel's war in Gaza, which has spurred both an increase in antisemitic hate crime as well as moves by conservative supporters of Israel led by President Donald Trump to brand pro-Palestinian protests as antisemitic. His administration has detained protesters of the war without charge and cut off funding to elite U.S. universities that have permitted such demonstrations.

In a post to X, a social network, Trump's deputy chief of staff Stephen Miller said Soliman had overstayed his visa and been allowed to work by the previous administration. He said it was further evidence of the need to "fully reverse" what he described as "suicidal migration."

Reuters was not able to independently verify the suspect's immigration status. When asked about Soliman, the Department of Homeland Security said more information would be provided as it became available.

VICTIMS BURNED

Brooke Coffman, a 19-year-old at the University of Colorado who witnessed the Boulder incident, said she saw four women lying or sitting on the ground with burns on their legs. One of them appeared to have been badly burned on most of her body and had been wrapped in a flag by someone, she said.

She described seeing a man whom she presumed to be the attacker standing in the courtyard shirtless, holding a glass bottle of clear liquid and shouting.

"Everybody is yelling, 'get water, get water,'" Coffman said.

Senate Minority Leader Chuck Schumer, a prominent Jewish Democrat, said it was an antisemitic attack.

"This is horrifying, and this cannot continue. We must stand up to antisemitism," he said on X.

The attack follows last month's arrest of a Chicago-born man in the fatal shooting of two Israeli embassy employees in Washington, D.C. Someone opened fire on a group of people leaving an event hosted by the American Jewish Committee, an advocacy group that fights antisemitism and supports Israel.

The shooting fueled polarization in the United States over the war in Gaza between supporters of Israel and pro-Palestinian demonstrators.

Colorado Governor Jared Polis posted on social media that it was "unfathomable that the Jewish community is facing another terror attack here in Boulder."