WASHINGTON, June 2, 2025 (AFP) - Several people suffered burns and other injuries Sunday in the US state of Colorado in what the FBI called a "targeted terror attack" against demonstrators seeking the release of Israeli hostages held in Gaza.

Police in the city of Boulder said a man was taken into custody. They were more cautious in presuming a possible motive for the attack, which multiple sources said was committed against members of the Jewish community during a peaceful gathering.

Local media cited eyewitnesses describing a man throwing something resembling a homemade Molotov cocktail at the group.

In one video apparently of the attack, a shirtless man holding clear bottles in his hands is seen pacing as the grass in front of him burns.

He can be heard screaming "End Zionists!" "Palestine is Free!" and "They are killers!" towards several people in red t-shirts as they tend to a person lying on the ground.

Other images showed billowing black smoke above a park.

"We are aware of and fully investigating a targeted terror attack in Boulder, Colorado," FBI chief Kash Patel said on X.

The White House said President Donald Trump has been briefed on the incident.

Asked if it was a terror attack against the protesters, Boulder Police Chief Steve Redfearn insisted it was "way too early to speculate motive" behind the violence, which took place shortly before 1:30 pm (1930 GMT).

He told reporters that "initial callers indicated that there was a man with a weapon and that people were being set on fire."

"When we arrived, we encountered multiple victims that were injured, with injuries consistent with burns and other injuries," Redfearn said.

Police on the scene "immediately encountered that suspect, who was taken into custody without incident," he added.

- 'Antisemitic attack' -

The Anti-Defamation League, a Jewish activist group, said on X that the attack occurred at Sunday's "Boulder Run for Their Lives" event, a weekly gathering of the Jewish community in support of the hostages seized during Hamas's attack on Israel on October 7, 2023, sparking the war in Gaza.

Israel's ambassador to the United Nations, Danny Danon, voiced outrage at the incident.

"Terrorism against Jews does not stop at the Gaza border -- it is already burning the streets of America," he said in a statement, describing how people marching for the return of hostages were attacked by someone "throwing... Molotov cocktails."

"Make no mistake -- this is not a political protest, this is terrorism."

US Secretary of State Marco Rubio weighed in, like Patel describing the incident as a "targeted terror attack."

"Terror has no place in our great country," Rubio said.

Several organizations decried the apparent hate-fueled violence.

"Today, during a peaceful walk on Pearl Street in Boulder to raise awareness for the hostages still in Gaza, our community was targeted in a violent, antisemitic attack," the Israeli-American Council said in a statement.

"This is an attack on all of us -- and we will not stay silent," it added.

The Boulder violence comes almost two weeks after the fatal shooting of two Israeli embassy staffers outside a Jewish museum in Washington, where a 31-year-old suspect who shouted "Free Palestine" was taken into custody by police.