Explained | What we know about the attack against Jewish demonstrators in Colorado

Authorities said they were investigating an attack in Boulder, Colorado, on Sunday as an act of terrorism, after a man used a "makeshift flamethrower" to attack demonstrators honoring Israeli hostages in the Gaza Strip.

Six people were hospitalized with burns and other injuries, and two of them were in serious condition, officials said.

Witnesses said the man threw an incendiary device into the crowd in a downtown pedestrian mall, according to authorities. The suspect, identified as Mohamed Sabry Soliman of Colorado Springs, yelled "Free Palestine" during the attack, the witnesses said. Soliman, 45, had not been charged as of late Sunday night.

The attack may intensify deep unease in the Jewish community in the United States. In recent months, two Israeli Embassy aides were killed in Washington, and a man set fire to the residence of Gov. Josh Shapiro of Pennsylvania, who is Jewish.

Here's what we know:

The attack targeted a peaceful event.

The victims, who range in age from 67 to 88, were participating in a weekly event called Run for Their Lives that is held in cities around the world, including Boulder. It is designed to call attention to the Israeli hostages taken by Hamas in the Oct. 7, 2023, terrorist attacks.

Police began to receive calls about an emergency on the Pearl Street Pedestrian mall near Boulder's county courthouse at 1:26 p.m., Boulder's police chief, Steve Redfearn, said at a news conference Sunday evening.

Initial reports mentioned a man with a weapon and people being set on fire. Redfearn said investigators were not entirely sure what happened, but that the reports were "fairly consistent with the injuries that we found on scene."

Video verified by the news agency Storyful showed a man, shirtless and holding two bottles, shouting while patches of grass burned in front of the courthouse and bystanders helped injured people.

Lisa Effress, who was eating lunch nearby Sunday, said that she ran to the scene after the attack. She saw smoke, people who were half-dressed and dazed, and discarded clothes that had been used to extinguish flames.

"It was horrible," Effress said.

Officials said four of the victims were taken to a hospital in Boulder and two were flown by helicopter to a burn unit in Denver. The victims' injuries ranged from minor to serious.

The FBI says the attack was a 'targeted act of violence.'

Soliman was taken into custody after witnesses pointed him out, Redfearn said.

The FBI was investigating the attack as an act of terrorism, Redfearn said, adding that the preliminary facts made it "clear that this is a targeted act of violence."

Late Sunday, police and the FBI had cordoned off a residential block in Colorado Springs with patrol cars. They let a woman enter a home identified as the attacker's.

Authorities will decide in the coming days what charges to file against Soliman and in what courts, Michael Dougherty, the district attorney for Boulder County, said at the news conference.

There was no immediate indication that Soliman was linked to any particular group or network, according to Mark Michalek, the special agent in charge of the FBI's Denver field office.

The attorney general of Colorado, Phil Weiser, a Democrat, said in a statement that the attack "appears to be a hate crime given the group that was targeted."