The FBI says a weapon it believes was used to kill popular American right-wing influencer Charlie Kirk has been found, however the killer remains at large.

The 31-year-old conservative activist was shot while addressing a crowd of about 3,000 people at Utah Valley University in Orem, south of Salt Lake City, just after midday on Wednesday, local time.

FBI Special Agent in Charge Robert Bohls told the media the weapon believed to have been used in the shooting was a high-powered bolt action rifle.

“[It] was recovered in a wooded area where the shooter had fled,” he told a press conference on Thursday, local time, adding the FBI laboratory would be analysing the weapon.

He said investigators also had images of the suspect, and were analysing “footwear … a palm print and forearm imprints”.

Special Agent Bohls said the bureau was yet to determine a motive.

He said the FBI had already received more than 130 tips, adding all leads were being “fully investigated”.

Investigators are treating the attack as a “targeted event”, he said.

“We don’t believe the community is at risk,” he said.

Beau Mason, the commissioner at the Utah Department of Public Safety, said the shooter “blended in” and “appears to be of college age”.

He said investigators had tracked the movements of the suspect who arrived on campus at 11.52am before making his way up a stairwell to the shooting location.

“[After the shooting] he moved to the other side of the building, jumped off of the building and fled off of the campus into a neighbourhood,” he said.

Mr Mason said investigators had “good video footage” of the suspect, but would not release it at this time.

“We’re working through some technologies and some ways to identify this individual,” he said.

“If we are unsuccessful, we will reach out to you as the media, and we will push that publicly to help us identify them.”

Police and federal agents mounted an intense manhunt on Thursday for the sniper who fired the single gunshot that killed Mr Kirk as he was fielding questions about gun violence.

Speaking at a Pentagon memorial service on Thursday to mark the September 11 terrorist attacks, US President Donald Trump announced he would award Mr Kirk a posthumous Presidential Medal of Freedom.

He praised Mr Kirk as a “giant of his generation, a champion of liberty and an inspiration to millions and millions of people”.

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