A man shouted “free Palestine” and used a “makeshift flamethrower” during an attack in Boulder, Colorado, that injured six people marching to bring awareness of Israeli hostages held by Hamas, officials said.

The suspect was identified as Sabry Soliman, 45, who was taken into custody at the scene, Mark Michalek, special agent in charge of the FBI’s Denver office, said in a news conference Sunday evening. The assault was being investigated as an act of terrorism, he said

The injured range in age from 67 to 88. The worst of the six was described by Michalek as being in critical condition; Boulder Police Chief Stephen Redfearn earlier said the rest had minor injuries.

They were at or near a weekly demonstration to support awareness of Israeli hostages still held in Gaza by Hamas militants, officials said.