The man accused of assassinating Charlie Kirk had expressed opposition to the conservative activist's views and indicated that he was responsible for the shooting, authorities said Friday as they announced an arrest in the killing that raised fresh alarms about political violence in a deeply polarised United States.

Tyler Robinson, 22, had become "more political" in the run-up to the shooting and mentioned during a dinner with family that Kirk would be visiting Utah, Gov Spencer Cox told a news conference. The governor cited as evidence engravings on bullet casings found in the rifle that authorities believe was used in the attack, as well as chat app messages attributed to the suspect that a roommate shared with law enforcement.